This is from an email. I thought it might be worth posting. A person is confused about the command to "repent and believe" and the idea that the Gospel isn't about "getting it right" but about Jesus getting it right for us, which we passively rely on as a gift.
...in the context you describe with Peter's preaching, you can think of repentance there as a change in the person's attitude toward the idea that they can save themselves. Notice that I did not say it means that I completely cease from ever trying to save myself by my own efforts. [All of us constantly fall back into it, but when we realize it we don't have to cognitively *do* something. The realization is what brings us running back to Jesus.]
"Repenting and believing" is by definition *not* about "having it right." Back when I really struggled with this, there were two texts that really served as litmus tests for me. One was Romans 4:4-5 and the other Galatians 2:21.
"Now to the one who works, his wages are not counted as a gift but as his due. And to the one who does not work but believes in him who justifies the ungodly..." (Romans 4:4-5)
See how Paul sets two ideas in complete contrast? There is the one working... and what he gets can't be called a "gift." When I get paid from my employer, I never say "Oh, thanks! You are so generous and gracious!" In complete contrast is the one who "does *not* work but believes in him..." Paul is saying that believing in "him who justifies the ungodly" is non-effort, is not about having it right but is relying upon the promise of "Him who justifies the ungodly." Paul is using the example of Abraham. God promised Abraham, "I will do this." Abraham relied on him to carry it out. Period.
Did Abraham do that perfectly? Nope. Paul brings up that in, I think, Galatians 3-4. That is what the whole deal about Sarah versus Hagar is. Do you remember the story? Years after God promised Abraham that he would have a son and be the "father of many nations," still nothing happened. So Sarah gave Abraham her handmaid, Hagar. Maybe they thought, "well... if we're supposed to have a son, maybe we should help God out and find a way to do it ourselves." So, Abraham impregnated Hagar and she had his son Ishmael. But that was not the son that God promised Abraham. Isaac came later, through his wife Sarah, just like God promised. What Paul does in that passage is contrasts Hagar and Sarah and their sons, one the product of human effort and the other the product of "promise." The first is "let's try to do it and get it right," and the second is, "God promised, so I'm going to rely on His grace."
That is like all of us. The Christian life is not about avoiding sin (though obviously we don't want to just run around doing things our Best Friend hates). If anything, it is about constantly realizing the ways that we are trying to "have it right", dropping that, and running back to Jesus. [It is often not our "sin" that comes between us and Jesus but our supposed "goodness."]
Galatians 2:21 is the same idea:
"I do not nullify the grace of God, for if righteousness [right-ness] comes through the Law, then Christ died for no reason."
Paul is simply saying this: if dotting the i's and crossing the t's does anything to get you anywhere at all, *in any way at all*, then Jesus came down here and died in vain.
[I do not address the issue of rewards or the place of obedience which are, of course, important. I'm merely pointing out that it is not about "having it right." Even in our Gospel-obedience, it is not about getting it right or getting a good grade or preventing certain bad things from happening. It is about loving our God.]