Heidelberg Catechism 24.62

Chapter 24 — Lord's Day 24

Section 62. Q. 62: But why can't the good we do make us right with God, or at least help make us right with him? 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. Even the best we do in this life is imperfect and stained with sin.