1 Corinthians 9:20

“And unto the Jews I became as a Jew, etc.] That is, in religion; or with respect to some religious observances peculiar to the Jews, for he himself was really a Jew by nature; who became as one unto them in this sense, when he for their sakes circumcised Timothy at Derbe, or Lystra, purified himself at Jerusalem, shaved his head at Cenchrea, observed their sabbath, and abstained from some sorts of food forbidden in the law; and his end in so doing was, not to confirm them in such usages, but that he might hereby have the greater influence over them, and by little and little bring them off of these things, or, as he says, that I might gain the Jews; bring them over to Christ, and off of a…”

“I became as a Jew--in things not defined by the law, but by Jewish usage. Not Judaizing in essentials, but in matters where there was no compromise of principle (compare Act 16:3; Act 21:20-26); an undesigned coincidence between the history and the Epistle, and so a sure proof of genuineness. to them that are under the law, as under the law--in things defined by the law; such as ceremonies not then repugnant to Christianity. Perhaps the reason for distinguishing this class from the former is that Paul himself belonged nationally to "the Jews," but did not in creed belong to the class of "them that are under the law." This view is confirmed by the reading inserted here by the oldest…”

“And unto the Jews - In this verse, and the two following, Paul states more at length the conduct which he had exhibited, and to which he refers in 1 Corinthians 9:19. He had shown this conduct to all classes of people. He had preached much to his own countrymen, and had evinnced these principles there. I became as a Jew - I complied with their rites, customs, prejudices, as far as I could with a good conscience. I did not needlessly offend them. I did not attack and oppose their views, when there was no danger that my conduct should be mistaken. For a full illustration of Paul’s conduct in this respect, and the principles which influenced him, see the notes on Acts 16:3; Acts 18:18; Acts…”

“To the Jews I became as a Jew - Conforming myself in all things to their manner of thinking and living, so far as; I could with innocence. To them that are under the law - Who apprehend themselves to be still bound by the Mosaic law. As under the law - Observing it myself, while I am among them. Not that he declared this to be necessary, or refused to converse with those who did not observe it. This was the very thing which he condemned in St. Peter, Gal 2:14. 1 Corinthians 9:21”

“unto: Act 16:3, Act 17:2, Act 17:3, Act 18:18, Act 21:20-26 are under: Rom 3:19, Rom 6:14, Rom 6:15; Gal 4:5, Gal 4:21, Gal 5:18 1 Corinthians 9:21”