I think the journey from Egypt through Sinai and into the Land of Canaan teaches us so many practical lessons on obedience to God.
Mostly we are taught what a stubborn group of people the Israelites are as they constantly fight against God's leadership.
But for the first time in hundreds of years, the Israelites are re-learning who God is and what His character is like. From time to time we need to revisit who God is and what His character is like.
The incident at Meribah teaches us three important qualities about God's character.

I feel these are important characteristics to lock into because we often think we can hide ourselves or our sin from God, or that God won't really do all that punishment stuff, or even that their are degrees of sin, and as long as ours is not as bad as theirs, we are okay - not true.
Read Num.20.1-3
In verse 1 we are at the 40th year of wandering, the punishment for disobedience is coming to an end, and with Miriam's death that means the death of the entire generation of unbelievers except for Moses and Aaron.
Now for a second and even third generation of Israelites we find we have an established pattern of grumbling against Moses leadership and God's soveriegn control.

God is Sovereign

The people immediately doubt that God is in control. Despite all signs and miracles, they grew up with them, and they still missed the point.
Do we do that? Do we doubt under the worst circumstances that God can still accomplish anything? I wonder if God is ever let down by our disbelief? Often he wanted to wipe out the Israelites because of their disbelief, in fact it has taken this long to enter Canaan because of their disbelief.
The importance is God's will still continues to move forward, despite the Israelites, and God's will continues to move forward despite us in the church age.
But there are faithful, Moses and Aaron still believe in God and they turn to Him
And again the Lord provides.

His command, speak to the rock
There is still grace in action, a promise of water. There is still grace in action for us.

God is Serious

Often we have a tendency to worry about the end result, don't we? If I ask my son to clean his room, I don't care if everything is shoved under the bed, just so long as it looks clean.
But that is not God's economy. He is concerned with our growth, with the "how" more than the end result. It's never the end justify the means with God. It's more like the means will lead us to the end.
God told Moses and Aaron to speak to the rock. This would have provided and given glory to God in the process. Another miracle with God in control of everything.
Moses and Aaron bring forh the water okay, but not quite how God asked.
God provided water, enough for the entire community, but the ends did not justify the means. When Moses struck the rock, he was in essence taking credit for the feat.
Sometimes we want to be in control, we want to provide the results because we trust ourselves. But God is serious when he says I want you to trust me and do things my way.

Sin is very very serious. It does not matter who you are or how well you argue, you can't argue your way out of sin.
Look what happens, the two most righteous people in the Israelite camp. Yet despite their position, sin was still sin, and it was still punishable. From little white lies to genocide, sin is sin. God hates it all the same.

Each of us, praise God, are sinners saved by grace, or I hope we are. It was undeserved but God gave it anyway, and no matter how righteous we are we still sin, if that sin goes unrepented then it just may be that God says, because of your stubborness, you are going to miss out on this blessing or this part of my will.
What will we do tomorrow to give God the glory? Realize that He is in complete control of our lives, Believe what He promises us, and live our lives as best we can properly handling sin.