Unexpected Heirs

Intro: Theme/Topic (What’s the problem, the question, etc.)

Imagine growing up in a family where you never questioned that you belonged.

You have your mom’s smile. You have your dad’s stubborn streak. Your last name is on your birth certificate. You know who you are.

But one day, you get a phone call. There’s been a discovery at the hospital — medical records are conclusive — and the news is devastating: You were switched at birth!

The family you grew up in, the family you love, the family you’ve always assumed was yours — you’re not biologically theirs.

This isn’t just a captivating movie plot. It’s actually happened!

In 1978, two baby girls were accidentally switched in a Florida hospital nursery. Each girl went home with the wrong family. Each was raised, loved, and never questioned — for years — until the truth came out. And when it did, it raised a question nobody was prepared to answer: Which family does she truly belong to?

Now, most of us will never get a phone call like that. But there is a version of that question that every person in this room has to face — and the stakes are infinitely higher.

It’s not about which human family you belong to. It’s about whether you belong to God’s family.

Who truly belongs to God’s family?

And this is really the central question at the heart of Paul’s entire letter to the Galatians.

False teachers had infiltrated the churches in Galatia, insisting that Gentile believers needed to be circumcised and keep the law of Moses in order to truly belong to God’s people.

They were confident they were the true children of Abraham —

They had the bloodline, They had the circumcision, They had the law.

And they looked at these Gentile converts and said, “You’re not really in. Not yet.”

So Paul writes this letter to answer the question once and for all: Who truly belongs to God’s family? And in Galatians 4:21–31, he delivers his most stunning answer yet. Let’s read it together.

Scripture

Grab your Bibles and turn with me to Galatians 4:21-31. If you need to use a pew Bible, you’ll find today’s text on page 1157. Once you’re there, please stand with me if you are able and follow along with me as I read...

Galatians 4:21–31 ESV

Tell me, you who desire to be under the law, do you not listen to the law? For it is written that Abraham had two sons, one by a slave woman and one by a free woman. But the son of the slave was born according to the flesh, while the son of the free woman was born through promise. Now this may be interpreted allegorically: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar. Now Hagar is Mount Sinai in Arabia; she corresponds to the present Jerusalem, for she is in slavery with her children. But the Jerusalem above is free, and she is our mother. For it is written, “Rejoice, O barren one who does not bear; break forth and cry aloud, you who are not in labor! For the children of the desolate one will be more than those of the one who has a husband.” Now you, brothers, like Isaac, are children of promise. But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now. But what does the Scripture say? “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman.” So, brothers, we are not children of the slave but of the free woman.

This God’s Word!

Prayer

Father as we spend time in Your Word this morning, give us the tastebuds to taste and see and to know that You are good! We ask this in Jesus’ name — Amen!

Intro: Formal (give context to passage, setting the scene, big idea)

Throughout this letter, Paul has been building one relentless argument…

Back in chapter 3, he asked the Galatians point-blank: “Did you receive the Spirit by works of the law, or by hearing with faith?”

And then he took them on a tour through Abraham’s story… Through the purpose of the law… Through the coming of Christ — All to prove that:

Belonging to God’s family has never been about what you can produce for God… It has always been about receiving what God has done for you.

Now here in chapter 4, Paul reaches the climax of that argument. And he does something nobody saw coming. He takes the story of Abraham’s two sons —

A story every Jewish person knew by heart… A story the false teachers almost certainly used to support their case — And he turns it completely on its head.

So who truly belongs to God’s family?

And here’s how Paul answers this question in our text today:

God’s children are those who receive what only God can give — not those who try to produce it for Him.

That’s the heartbeat of this passage. And Paul develops it in three moves.

In verses 21-25, he exposes the confident insiders — Those who were sure they belonged but were tragically wrong.

Then, in verses 26-28, he reveals the unlikely heirs — The outsiders no one expected God to claim as His own.

And finally, in verses 29-31, he delivers the verdict — There is no shared inheritance between self-effort and grace. You’re either in one family or the other.

So let’s look at Paul’s first move.

The Confident Insiders

Paul wastes no time. He looks at those who want to be under the law and says, “You want to appeal to the law? Fine — let’s actually listen to what the law says.” And then he uses their own authority to dismantle their entire case.

In verse 22, Paul takes us back to the story of Abraham’s two sons and the two different mothers they were born to. You can read the full account on your own later in Genesis 16–21, but here’s what you need to know.

God had promised a son to Abraham and Sarah. And through that son, God’s blessing would come to the nations. And that blessing was nothing less than the very favor and presence of God Himself.

The only problem was that Abraham was 100 years old and Sarah his wife was 90. Oh — and one other little thing… she was barren!

So Abraham and Sarah found themselves in a humanly impossible situation. And in a way, they believed God’s promise.

But their actions would show that they believed God needed their help to make good on that promise.

So they found what looked like a workaround — a way to get God’s promise through the back door.

In that culture, it was legally permissible — though God did not approve — For a husband to conceive a child through his wife’s slave woman. So they took matters into their own hands in what amounts to trying to seize God’s promise by means of their own self-reliance.

And a son was born. Ishmael was his name. And in verse 23, Paul says he was born “according to the flesh.”

Paul’s point: Ishmael was the product of human effort to fulfill God’s promise for Him.

Now this is very interesting — because in Genesis 17, after Ishmael has already been born, God tells Abraham that He is still going to give him a son through Sarah. And Abraham actually pushes back. look what he says to God in verse 18:

Genesis 17:18 ESV

And Abraham said to God, “Oh that Ishmael might live before you!”

Do you hear what Abraham is saying here? He’s saying…

“God, isn’t what I’ve done good enough? Can’t you just accept what I’ve produced? Do I really need you to do something I can’t do myself?”

Church, this is the human heart on full display… We would rather present God with something we manufactured than stand before Him empty-handed and trust Him to provide. We are that allergic to grace!

But even after Abraham pushes back, God says no. I will still give you a son through Sarah.

And God did what was humanly impossible — He gave a son to a barren woman in her nineties. And Abraham learned that the only acceptable response to God’s merciful promise is to trust that promise.

Paul makes this contrast crystal clear in verse 23:

The slave woman gave birth as a result of human self-reliance. The free woman gave birth by the power of the Spirit as a result of God’s promise.

One relies on human effort to keep God’s promise. The other trusts God to give it.

And here’s what makes this so uncomfortable for us. The Hagar plan doesn’t look like rebellion.

It looks responsible. It looks resourceful.

Abraham and Sarah didn’t reject God — They just decided He needed their help.

And that is exactly what we do when we add our own performance to the gospel. We’re not rejecting Christ — We’re just making sure we do our part too. Just in case grace isn’t enough. Just in case what God has done needs a little something from us to really work.

Now in verse 24, Paul interprets this story and applies it to the churches in Galatia. He says this story can be understood allegorically. Let me pause here to say three quick things:

Paul’s allegorical interpretation of these events does not mean they weren’t historical.

Just because Paul uses allegory here does not give us license to allegorize anything we want to in Scripture.

Paul could do this because he was writing Scripture under the inspiration of the Holy Spirit — And that means we receive this interpretation with full confidence because God Himself stands behind it.

Now these false teachers would have known this story inside and out. And they almost certainly used it to make their case. It probably went something like this:

“We are descended from Sarah’s son Isaac. We have the law given at Mt. Sinai. We have circumcision. We keep the food laws. We are the insiders.”

And by contrast, they would have looked at these Gentile Galatians — uncircumcised, law-ignorant outsiders — and applied Hagar to them.

Now watch what Paul does… He says the two women represent two covenants — Two different ways of relating to God. One of them is from Mount Sinai, where the Mosaic law was given. Now immediately the false teachers would see themselves in this category — Sinai is theirs. But Paul says the woman from Sinai bears children for slavery. And it’s not Sarah — It’s Hagar!

Then Paul adds this detail — Mount Sinai is in Arabia. Arabia is outside the Promised Land. So where these false teachers believed they were the insiders, members of God’s family — Paul is saying, spiritually speaking, you are the outsiders.

And then he doubles down. He says the slave woman also corresponds to the Jerusalem of Paul’s day —

The temple, the sacrificial system, the entire religious establishment.

All the things these Jewish false teachers were clinging to for their identity — Everything they depended on to make them right with God — Paul puts it all in the category of slavery, with Hagar and Ishmael. Not with Sarah and Isaac.

They were confident they were children of Sarah. But Paul says they are children of Hagar.

They had every external credential going for them —

the bloodline, circumcision, the law, the temple.

And Paul says it all amounts to slavery. Because self-effort to produce what only God can give never leads to freedom. It only leads to bondage.

But if the confident insiders aren’t the true heirs — then who is? That’s where Paul goes next.

The Unlikely Heirs

But now Paul lifts our eyes. From the present Jerusalem — enslaved, bound to self-effort — and he points us upward to the Jerusalem above. And he says, “She is free. And she is our mother.”

While the Jerusalem below is in slavery with her children, the Jerusalem above is free — because her children trust and receive the promise of God.

And she is our mother, Paul says.

Now this was just as shocking as Paul applying the slave woman to the Jewish false teachers — it’s just the other side of the shock.

The false teachers would have naturally applied Hagar to these uncircumcised Gentiles. But Paul applies the free woman Sarah and the Jerusalem above to them. She is our mother.

Now this is interesting because in a place like Psalm 87, Zion — the city of God — is depicted as a mother to many who are born from other nations outside of Israel. Which means that including non-Jewish people in God’s family was always part of God’s plan — not some late invention in the New Testament.

Next, in verse 27, Paul reaches back to the prophet Isaiah to show that this was always God’s design — that the barren, desolate woman would end up with more children — more blessed than anyone imagined.

This is a prophecy of God’s ultimate and final restoration — a forever dwelling place for God’s people. And the contrast is stark: God will bring life from barrenness.

And Paul applies this to the Galatian believers and to all who trust Jesus to do for them what they could never have done for themselves.

This is the logic of the gospel: What is humanly impossible — Dead sinners made alive… Outsiders made heirs… The undeserving welcomed in — And it’s God who accomplishes all this by His power!

And notice that barrenness is a theme that runs all throughout Scripture.

Sarah was barren — and God gave her Isaac. Rebekah was barren — and God gave her Jacob. Rachel was barren — and God gave her Joseph. Hannah was barren — and God gave her Samuel. Elizabeth was barren — and God gave her John the Baptist.

God is telling us something. And it’s this: God is in the business of doing the humanly impossible to bring about His good promises.

And then God outdoes Himself. The ultimate fulfillment of His promise came not merely through a barren woman — but through a virgin.

As if God was saying, “You thought barrenness was impossible? Watch this.” It is medically impossible for a virgin to give birth. And yet that is exactly what God did.

And notice something about every single one of these stories. God never works around the impossibility. He works through it. He doesn’t find a detour around the barrenness. He makes the barren woman the mother.

And now Paul says it plainly. No more allegory. No more typology. Just a direct announcement over these Gentile believers: “Now you, brothers, like Isaac, are children of promise.”

Not children of effort. Not children of circumcision. But children of promise.

Because they didn’t cling to what they could produce on their own — they received what only God could give.

Just as Isaac’s birth was a supernatural work of the Spirit, so too was the Galatians’ membership in the family of God. Their identity was declared, not earned. Their belonging rested entirely on what God had done — Not on what they could produce.

And today God’s family is still open to anyone who will lay down what they can produce on their own to receive what only God can give.

God gave us His Son — born of a virgin, who lived, died, and rose again on the third day — to pay for all your sins and make you right with God. Adopted into His family by faith alone in Jesus.

This is good news for everyone in this room who has wondered if they truly belong to God’s family but deep down have no assurance.

You come to church. You read your Bible and pray. Maybe you’ve been baptized. You volunteer. You give. You serve. You’re a good parent. A faithful spouse. A decent person. But still you wonder — is it enough?

The bad news is you haven’t done enough — and you never will. Nobody can.

And maybe you’re on the other end of this. You’re not wondering if you’ve done enough — you know you haven’t.

You’re carrying shame from things you’ve done that you think disqualify you from ever being part of God’s family.

But remember what we just saw — God chose the barren woman. He works through impossibility. Your emptiness isn’t a disqualification. It’s exactly the condition God uses!

The only way to know that you are a citizen of the Jerusalem above is to lay down what you can produce on your own and receive what only God can give you:

The forgiveness of your sins. And the favor and presence of God in your life.

You can do this right now by praying a simple prayer right where you are, from your heart. Something like:

God, I’ve tried everything I can think of to earn Your favor, but it was never enough. I can’t save myself. I can’t even help. I need You, Jesus, to pay for my sins and make me part of Your family. Forgive me now by faith alone in Christ alone, who died and rose again for me — Amen!

If you prayed that from your heart today, then what Paul says in verse 28 is true of you. You, like Isaac, are a child of promise. You are part of God’s family. And nothing can ever take that from you.

That’s worth celebrating. I’d love to know if you prayed with me today so I can celebrate with you and encourage you. Please come find me — I’ll be by the front doors after the service.

So far Paul has exposed the confident insiders and revealed the unlikely heirs. But can these two families coexist? Can you have a foot in each? Paul’s answer is swift and final. Let’s look at his verdict.

The Verdict

Earlier I said we’re naturally allergic to grace. But it goes even deeper than that. Not only are those addicted to self-effort allergic to grace — They are actively hostile to it. And that hostility is exactly what Paul addresses first in his verdict.

In verse 29, Paul points to the fact that Ishmael persecuted Isaac. And he says those born according to the flesh always persecute those born according to the Spirit.

Now the false teachers weren’t violently persecuting the Galatian believers. They were trying to make them slaves again by pressuring them to rely on law-keeping and circumcision.

But why? Why are people who rely on self-effort so hostile to grace?

Because the gospel is offensive. It insists that your very best — the thing you’re most proud of — doesn’t move the needle of God’s acceptance of you, one bit!

And people’s insecurities make them hostile — because if grace is true, then everything they’ve built their lives on counts for nothing.

So people don’t just disagree with the gospel — they need to suppress it, because its very existence is a threat to their entire system of self-justification.

And this pattern didn’t end in the first century. Wherever the gospel of grace is proclaimed, there will be people who oppose it. Sometimes this comes from outside the church. But it often comes from within — not from atheists but from religious people who have built their identity on their own performance.

This is the pattern:

Flesh persecutes Spirit. Self-effort is never content to coexist with grace — it has to attack it. And that brings Paul to his sentence.

In verse 30, Paul reaches back to Genesis 21 and quotes Sarah’s own words to Abraham: “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman.”

And the key word is inherit. Because the whole issue is: Who are the rightful heirs of God’s promise to Abraham?

And the verdict is that there can be no shared custody of this inheritance. You cannot combine self-effort and grace. You cannot supplement the promise with your own production. There is no blended family here.

And “cast out” is hard language. But Paul means it to be — because what’s needed is not gentle tolerance of this false teaching but a decisive rejection of it.

This is not a rejection of people made in God’s image — but a rejection of a false gospel that enslaves.

These Galatians must refuse to submit to the false teachers’ demands. Because it’s the false teachers who are the outcasts with respect to the inheritance — while these Gentile believers are the ones welcomed in.

And then Paul lands his final declaration in verse 31: “So, brothers, we are not children of the slave but of the free woman.”

That’s it. That’s Paul’s closing statement. No qualifications. No exceptions. No fine print.

We are not children of the slave. We are children of the free woman. That is who you are if you have received what only God can give.

So what does this mean for you, church?

It means you must refuse to let anything other than Jesus’ work for you determine your standing before God.

And this is both an external and an internal battle.

Externally, we must reject any teaching that adds conditions to the gospel — any voice that says faith in Christ is necessary but not sufficient.

That might be a preacher on television. An influencer on YouTube. It might even be a well-meaning friend who tells you that you need to do more to be sure you’re really saved.

Internally, we must shut down that inner voice that whispers, “Yes, Jesus did His part — but are you doing yours? Are you reading enough? Praying enough? Serving enough? Are you really committed enough for God to accept you?” That voice is the false teacher in your own heart. And Paul says: cast it out!

So let me ask you directly: Are you functionally living as a child of the slave woman today? Not because you’ve rejected Christ — but because you’ve quietly added your own performance to Christ’s finished work.

Maybe it looks like this: Your assurance before God rests more on your church attendance record than on Christ.

Or maybe this: You intellectually affirm grace — you’d say all the right things in a Bible study — but emotionally, you cannot stop trying to earn God’s favor.

If that’s you, the answer is the same as it was for Abraham: Stop producing. Start receiving.

Conclusion/Response (Gospel & Repent/Believe)

We started this morning with a question. We imagined what it would be like to discover you’d been switched at birth — to find out that the family you always assumed was yours isn’t really yours at all.

Paul does something far more shocking in this passage. He takes people who were absolutely certain they belonged to God’s family — people with every credential, every reason for confidence — and he tells them they’re in the wrong family.

And then he turns to a room full of nobodies — people with no pedigree, no birthright, no resume to present — and he says, “You are the heirs. You are the children of promise.”

Who truly belongs to God’s family? Not those who try to produce for God what only God can give — but those who receive it. Empty-handed. With nothing to offer.

So whatever you’re clinging to this morning — whatever you’ve been manufacturing and holding up to God and saying, “Isn’t this enough?” — lay it down. Because as the old hymn says:

“Nothing in my hands I bring — simply to the cross I cling.”

Let’s pray.

Prayer

Father, help us to stop producing and start receiving. Teach us to come to You with empty hands — and to trust that what You give is more than enough. In Jesus’ name — Amen.

Closing Song: “For Freedom Christ Has Set Us Free”

Closing Words:

What a fitting song to sing after being in Galatians 4 today. Christ has set us free — and Paul says in the very next verse, Galatians 5:1 “stand firm therefore, and do not submit again to a yoke of slavery.” That’s our charge as we leave today.

Gospel Appeal:

If today you heard the gospel for the first time and something stirred in your heart — or if you’ve heard it many times but today it finally broke through — I want you to know that the invitation still stands. Come to Christ right now with nothing in your hands. You don’t need to clean up first. You don’t need to figure everything out. You just need to receive what only God can give. If that’s you today, there will be some people up front here after the service who would love nothing more than to talk with you and pray with you.

Next Steps:

And for those of you who are already children of the free woman — maybe today exposed something. Maybe you realized that somewhere along the way you started adding your own performance back to the gospel.

Here’s a simple next step: tell someone this week. Find a trusted brother or sister — maybe someone in your small group, maybe your spouse — and say, “I’ve been living like a child of the slave woman, and I want to stop.” That one honest conversation can be the beginning of real freedom.

Missional Charge:

Now as we go, remember — you’re going to encounter people this week who are exhausted from trying to earn their way to God. They may not use those words. They may not even know that’s what they’re doing. But they are weary and they are enslaved. And you carry the answer. You know what only God can give. So look for the opportunity to share it — to share the same grace that set you free!

Benediction: Jude 24–25

Now to him who is able to keep you from stumbling and to present you blameless before the presence of his glory with great joy, to the only God, our Savior, through Jesus Christ our Lord, be glory, majesty, dominion, and authority, before all time and now and forever. Amen.