This is from a Don Carson talk entitled “What is the gospel and how does it work? Part 2”.
How do you know that you’ve done enough — to testify that the saving grace of God that has justified you and has given you new birth, has transformed you enough so that you know that your profession of faith is credible?
How do you know?
Listen. The ground of your acceptance before God is always the cross. It’s always Christ. It’s always Christ. It’s always Christ. Nothing but Christ.
When you get to heaven if, as it were, Saint Peter stands at the door and says “Why should I let you in here?” your answer is not “Well, you know, I think there are quite a lot of evidences that I have been born again”. Your answer is “I have no other argument, I need no other plea. It is enough that Jesus died, and that he died for me.”
God sent forth Christ to be the propitiation for our sins. My confidence is there. On the other hand there will be some evidence that you have been transformed and I love the way [John] Newton … puts it. He says, “I am not what I used to be. I am not what I want to be. I am not what one day I will be. But I am not what I was, and by the grace of God I am what I am”.
That’s how Christians continue to walk in humility, looking at the changes that God has made, deeply ashamed of the things that still need changing as we press on for the final transformation still to come.