I think that some of the other interpretations are pretty correct in saying that this is a religious song. I would just like to elaborate on one line:

"The beauty of grace is that it makes life not fair."

At first, I didn't understand the line, until one day in religion class, I was dozing off until my teacher mentioned "grace". As she explained it, I began to understand...

Grace is the gift that God gives us--the unconditional love, that he will have for us no matter what.

Saying that grace is unfair is pretty true. Whether you're a bad sinner or you rarely do things wrong, God will love you the same. And that's the beauty of it. =D