Acts 15:1

And certain men which came down from Judea
To Antioch; they were not sent by the apostles, they came down of "themselves"; who they were, is not certain; that they were "judaizing" Christians, and teachers among them, is plain from the following account: according to Epiphanius ^F7 they were Cerinthus, and some of his followers: these

taught the brethren;
the Gentile converts at Antioch, who are styled "brethren", though they were Gentiles, because they were regenerated by the grace of God, and were of the same faith with the believing Jews, and in the same church state with them at Antioch: and said,

except ye be circumcised after the manner of Moses;
or custom of Moses, which had been used from the time of Abraham, and was revived and reinforced by Moses; wherefore the Syriac version renders it, "the law of Moses"; (See Gill on John 7:19)

ye cannot be saved;
these men were not only for retaining circumcision, which was now abolished, but they made it necessary to salvation; which was carrying the matter further than even the unbelieving Jews themselves did, at least some of them: for though indeed it is a notion with them, that no circumcised persons go to hell, but are all saved; and some of them say, that God rejects uncircumcised persons, and brings them down to hell ^F8; yet others of them speak of the godly among the nations of the world, and of the proselytes of the gate, who keep the seven precepts of Noah, as persons that shall be saved; so Ananias the Jew, preceptor to King Izates, when he signified his great desire to be circumcised, in order to put him off of it, told him, that if he was determined to follow the customs of the Jews, he might worship God without circumcision, which was more peculiar to the Jews than to be circumcised ^F9.