By the grace of God I am what I am, and his grace toward me was not in vain. On the contrary, I worked harder than any of them, though it was not I, but the grace of God that is with me.
1 Corinthians 15:10
Check out this daily devotional by John Piper: http://www.desiringgod.org/articles/we-work-by-grace . It rocked my world!