St. Thomas Aquinas on Galatians 6:1-5

Brethren, and if a man be overtaken in any fault, you, who are spiritual, instruct such a one in the spirit of meekness, considering thyself, lest thou also be tempted. 2 Bear ye one another’s burdens; and so you shall fulfil the law of Christ. 3 For if any man think himself to be something, whereas he is nothing, he deceiveth himself. 4 But let every one prove his own work; and so he shall have glory in himself only and not in another. 5 For every one shall bear his own burden.

After leading the Galatians back to the state of truth as to divine things, the Apostle then leads them back as to things human, instructing them how to behave toward men. First, how to act toward the upright; Secondly, toward those who are wicked (v. 11).

With respect to the first, he does three things: First, he teaches how superiors should act toward inferiors; Secondly, how equals toward equals (v. 2); Thirdly, how inferiors toward superiors (v. 6).

Regarding the first he does two things: First, he sets forth the admonition; Secondly, he assigns the reason for the admonition (V. 1): considering thyself, lest thou also be tempted.

Therefore, because he had said so much about sin, then, lest anyone free of sin be severe toward sinners, he gives them an admonition about meekness and mercy, saying: Brethren, and if a man be overtaken in any fault, you, who are spiritual, instruct such a one in the spirit of meekness. Herein he lays down the three elements which form the admonition.

The first consists in being come upon unawares. For when some sin out of malice, they are less worthy of forgiveness: “Who as it were on purpose have revolted from him and would not understand all his ways” (Job 34:27). But when one is overtaken by temptation and lured into sin, pardon should be granted him more readily. That is why he says, and if a man be overtaken in any fault, i.e., fall through want of circumspection and because of trickery, so that he could not escape, instruct such a one in the spirit of meekness.

The second is infrequency of sin. For some sin as a matter of custom: “Cursing and lying and killing and theft and adultery have overflowed and blood hath touched blood” (Hos 4:2). Against such sinners more severe measures should be taken. And this is excluded when he says, in any, implying that he is speaking of those who do not sin as a daily practice.

The third is the quality of the sin. For some sins consist in commission and some in omission. And the first is more grave than the second, because the former are opposed to negative precepts which bind always and at every moment; whereas the latter, being opposed to affirmative precepts, since they do not bind one at every moment, it cannot be known definitely when they do bind. Hence it is said in Psalm 18 (13): “Who can understand sins?” And touching this he says, in any fault. Or, according to a Gloss, a fault is a sin committed through ignorance.