До галатів 3:3

begun--the Christian life (Phi 1:6). in the Spirit--Not merely was Christ crucified "graphically set forth" in my preaching, but also "the Spirit" confirmed the word preached, by imparting His spiritual gifts. "Having thus begun" with the receiving His spiritual gifts, "are ye now being made perfect" (so the Greek), that is, are ye seeking to be made perfect with "fleshly" ordinances of the law? [ESTIUS]. Compare Rom 2:28; Phi 3:3; Heb 9:10. Having begun in the Spirit, that is, the Holy Spirit ruling your spiritual life as its "essence and active principle" [ELLICOTT], in contrast to "the flesh," the element in which the law works [ALFORD]. Having begun your Christianity in the Spirit, that is, in the divine life that proceeds from faith, are ye seeking after something higher still (the perfecting of your Christianity) in the sensuous and the earthly, which cannot possibly elevate the inner life of the Spirit, namely, outward ceremonies? [NEANDER]. No doubt the Galatians thought that they were going more deeply into the Spirit; for the flesh may be easily mistaken for the Spirit, even by those who have made progress, unless they continue to maintain a pure faith [BENGEL].

The apostle in this chapter, I. Reproves the Galatians for their folly, in suffering themselves to be drawn away from the faith of the gospel, and endeavours, from several considerations, to impress them with a sense of it. II. He proves the doctrine which he had reproved them for departing from - that of justification by faith without the works of the law, 1. From the example of Abraham's justification. 2. From the nature and tenour of the law. 3. From the express testimony of the Old Testament; and, 4. From the stability of the covenant of God with Abraham. Lest any should hereupon say, "Wherefore then serveth the law?" he answers, (1.) It was added because of transgressions. (2.) It was given to convince the world of the necessity of a Saviour. (3.) It was designed as a schoolmaster, to bring us to Christ. And then he concludes the chapter by acquainting us with the privilege of Christians under the gospel state.

3:3 by . . . human effort (literally by flesh): Paul makes a pun: The Galatians were trying to become perfect by human effort through keeping the law about circumcising the flesh of the male foreskin.