As Paul has led us to the fact and means of justification through the redemption that is in Christ Jesus, he now plays devil's advocate by asking if justification then violates the law. Justification, being the process by which God makes it "just as if" we had never sinned, gives the appearance that God simply disregards our sin. In response to his own question, Paul gives us 3 reasons why this is false and why justification does not violate the law, but in the end only establishes the perfection and divinity that is in the law.
