The other part of that is though, it seems we can work and work and work until we're blue in the face, all in our own efforts, and in the context of "eternity", it means nothing. "did we not do x,y,z?" "depart from Me, I never knew you".
So if faith produces good works, is it really me doing them (Paul said "I, yet not I"), or is it that I'm looking to Jesus the Author and Finisher of my faith, keeping me eyes on Him, yielding to His will, and then HE does the works through me? And how do know where that line is between "this is God working through me" vs. "this is me being a 'good' guy and earning my way"?
Personally, sometimes I think I can really tell when it's God working through me. Other times, I feel I struggle on my own strength.