Heidelberg Catechism - Lord's Day 24

62. Q . Why can’t our good works be our righteousness before God, or at least a part of our righteousness?
     A. Because the righteousness which can pass God’s judgment must be entirely perfect and must in every way measure up to the divine law. But even our best works in this life are imperfect and stained with sin.

63. Q . How can our good works be said to merit nothing when God promises to reward them in this life and the next?
     A. This reward is not earned; it is a gift of grace.

64. Q . But doesn’t this teaching make people indifferent and wicked?
     A. No. It is impossible for those grafted into Christ through true faith not to produce fruits of gratitude.