John Calvin Commentary Acts 11:2

"And when Peter was come up to Jerusalem, they that were of the circumcision contended with him," — Acts 11:2 (ASV)

They reasoned with him. Obstinacy usually accompanies error. This was now a fault containing too gross ignorance, in that they did not quietly receive the Gentiles into their fellowship, united to them by the same Spirit of faith. But they not only drew back, but also contended with Peter contentiously, and blamed him for his action, which deserved great praise. They heard that the Gentiles had embraced the Word of God; what hindered them then from embracing them, so that they might be joined together under the government of one God? For what more holy bond can there be than when all people, with one consent, are united and joined to God? And why should not those grow together into one body who make the Messiah of God their head? But because they saw the external form of the law broken, they thought that heaven and earth were collapsing.

And note that although Luke said before that the apostles and brethren had heard this news, yet he spoke nothing of offense; but he introduces now, as it were, a new group of men, who contended with Peter. The brethren, he says, heard, and that was all; it follows, When Peter was come to Jerusalem, those which were of the circumcision did contend with him, who were undoubtedly different from the first group. Again, these words “of the circumcision” (Greek: περιτομῆς), do not simply signify the Jews, but those who were too much devoted to keeping the ceremonies of the law.

For there were none from Jerusalem in Christ’s flock at that time, except only those who were circumcised. From whom, then, could he distinguish these men? Lastly, it seems unlikely to be true that the apostles, and those who were moderate among the faithful, attempted this confrontation.

For though they had been offended, yet they might have conferred with Peter privately, and have asked for a reason for his action. For these reasons, I am led to think that those are called “of the circumcision” who placed such great importance on circumcision that they granted no one a place in the kingdom of God, unless he took upon himself the profession of the law, and, being admitted into the Church by this holy rite, put off uncleanness.