WSC Q.82: Is any man able perfectly to keep the commandments of God?
No mere man since the fall is able in this life perfectly to keep the commandments of God, (Eccles. 7:20, 1 John 1:8,10, Gal. 5:17) but doth daily break them in thought, word, and deed. (Gen. 6:5, Gen. 8:21, Rom. 3:9–21, James 3:2–13)
WLC Q.149: Is any man able perfectly to keep the commandments of God?
No man is able, either of himself, (James 3:2, John 15:5, Rom. 8:3) or by any grace received in this life, perfectly to keep the commandments of God; (Eccl. 7:20, 1 John 1:8,10, Gal. 5:17, Rom. 7:18–19) but doth daily break them in thought, (Gen. 6:5, Gen. 8:21) word, and deed. (Rom. 3:9–19, James 3:2–13)
WCF 16.4.
They who, in their obedience, attain to the greatest height which is possible in this life, are so far from being able to supererogate, and to do more than God requires, as that they fall short of much which in duty they are bound to do. (Luke 17:10, Neh. 13:22, Job 9:2–3, Gal. 5:17)