Suppose you were explaining all of this to someone who didn't know what sin is. You had to explain sin to them because they just didn't know what you were talking about when you used the word. How would you explain it to them?
It's a little like this when we are having religions of the world explained to us, religions of which we are not a part. In the Buddhist religion they have a conception of dukkha. It's translated "suffering" into English, but Buddhists tell me that that simple transliteration doesn't capture the meaning completely.
I suspect Buddhists react the same way when Christian talk about sin. How would you make the idea clear to them?