"He has delivered us from the authority of darkness and transferred us to the kingdom of his beloved Son, in whom we have redemption, the forgiveness of sins." -Colossians 1:13-14
Paul declares here (and in Ephesian 1) that forgiveness is redemption. But redemption from what? We tend to be self focused and see sin as a wrong moral action on the part of some human. But what if sin is something far greater, like the authority of God's law and goodness being mocked and violated by you? Rape isn't merely a wrong action, it is the mockery and violation of something and someone highly valued by God. See the difference? From God's view each and every sin is the violation and dishonor of His authority—of His goodness—of all of the moral law (James 2:10). Do we usually think that way? No.
God's vision of the death of Jesus is much grander that just providing a way for those He loves to be forgiven and avoid hell. But isn't that what we usually think? Dishonor of the law is evil and that evil must be dealt with for God to reestablish goodness. And He as a good creator was responsible to not leave evil unresolved. A new creation was needed—one that honored the law and excluded dishonor of it. God did this in a way that is radical and surprising. He became part of His creation taking on our identity under law. He honored the law in its fullness in life and then took on death in the place of lawbreakers. In short, Jesus died the death of all men to establish the law in its glory and honor. The way God did this is something to celebrate because it is the ultimate revelation of the lavish righteous generosity of a good God—"by his knowledge my righteous servant will make many righteous." (Isaiah 53:11) This is the celebration of the lamb and all people are commanded and invited to discard their identity as unrighteous lawbreakers under the old creation and be clothed in the new creation where the finished work of Christ is full completeness. Amen? Are you persuaded?
A Christian cannot sin—he cannot dishonor the law--because Jesus honored the law in its fullness and every Christian is a member of the new creation in Christ where His identity as perfect is our identity and our identity as lawbreakers is gone because He took it away. Do you see this identity as real or merely as a get-out-of-jail-free card? To think this way does not mean that we pretend that Christians don't do what appears to be sin—to do things that are a violation of goodness, to do what is a evil: lying, stealing, adultery, coveting, strife, envy, pride, and much much more. Those are all evil for a Christian to do, but they are simply the fruit of forgetting the new creation—forgetting that only perfection counts with God. Let's be honest about both the beauty of our identity above the law and the evil of our actions that result from forgetting perfection.