Galatians 3:1

The apostle is here dealing with those who, having embraced the faith of Christ, still continued to seek for justification by the works of the law; that is, who depended upon their own obedience to the moral precepts as their righteousness before God, and, wherein that was defective, had recourse to the legal sacrifices and purifications to make it up. These he first sharply reproves, and then endeavours, by the evidence of truth, to convince them. This is the right method, when we reprove any for a fault or an error, to convince them that it is an error, that it is a fault. He reproves them, and the reproof is very close and warm: he calls them foolish Galatians, Gal 3:1. Though as Christians they were Wisdom's children, yet as corrupt Christians they were foolish children. Yea, he asks, Who hath bewitched you? whereby he represents them as enchanted by the arts and snares of their seducing teachers, and so far deluded as to act very unlike themselves. That wherein their folly and infatuation appeared was that they did not obey the truth; that is, they did not adhere to the gospel way of justification, wherein they had been taught, and which they had professed to embrace. Note, It is not enough to know the truth, and to say we believe it, but we must obey it too; we must heartily submit to it, and stedfastly abide by it.

— Matthew Henry's Concise Commentary (public domain)