The Westminster Shorter Catechism

Q82. Is any man able perfectly to keep the commandments of God?

A. No mere man since the Fall is able in this life perfectly to keep the commandments
of God,[1] but doth daily break them in thought, word, and deed.[2]

Proofs

[1] Ecclesiastes 7:20; 1 John 1:8, 10; Galatians 5:17;
[2] Genesis 6:5; 8:21; Romans 3:9–21; James 3:2–13.

Comments

To keep the commandments of God perfectly requires one with a nature that is perfectly holy, having no inclination to evil, to yield constant and uninterrupted obedience to all the commandments of God, whether in thought, word and deed.

Before the Fall, Adam, was such a person. His nature was mutable and he eventually fell, but he was created in righteousness (Ecc 7:29) and so was able to keep God’s commandments perfectly, to fulfil the condition of the Covenant of Works, which required perfect obedience. But since the Fall, no mere man is able to do this in this life (Ecc 7:20). Only the Lord Jesus Christ, who was fully God and fully man in one person, was able to keep the commandments perfectly though He was tempted at all points like as we are (Heb 4:15). He kept the commandments perfectly, that His righteousness might be imputed upon us; and then went to the Cross to pay the penalty for our sin, that we might be reconciled to God.

Because of what the Lord has done, however, all true believers, when they leave this present life, will be made perfect in heaven and will be enabled perfectly to obey God in whatsoever He shall require of them (cf. Heb 12:22–23).

Nevertheless, the saints on earth, having their hearts renovated, will desire to keep the commandments of God sincerely (cf. 2 Cor 1:12; Rom 7:23–24; 1 Jn 3:9), rather than taking delight and pleasure in sin as the unregenerate do. They ought to endeavour after perfection (Mt 5:48), and seek always to attain to higher and higher degrees of perfection, though they know that in this life they will never attain absolute perfection because of remaining corruption (Ps 130:3).