What does that mean?

Have you ever been talking with someone and just wanted to say, "What in the World does that mean?!?" I had an experience like that today, and Yes this will be about theology. So I was talking with a pastor and he was relating a story and within this story told me that if i was going to do what he did, I would need, prayer, fasting and to "make sure I was right with God." How can a Christian not be right with God if all of our past, present and future sin has been removed, and we are seen as Righteous, because of Christ's imputed righteousness? Heard this phrase many times from Christians, get right with God, and it seems what they are speaking of is to repent of the sin in our life. But when is our life without sin? If you understand the rhetorical nature of the question, you will see the problem here. We are either right with God or we aren't, God can't say, OH you sinned 5 min. ago now we aren't square, because Jesus squared everything at the cross.

So where did this term come from and why are we saying it?