Acts 15:5

But there rose up certain of the sect of the Pharisees
Which was the strictest sect of religion among the Jews:

which believed;
that Jesus was the Messiah, and professed their faith in him, and were members of the church, though they still retained many of their pharisaical tenets, and are therefore said to be of that sect: these rose up in opposition to Paul and Barnabas, as they were relating their success among the Gentiles, and giving an account of the difference that had happened at Antioch, and their own sense of that matter:

saying, that it was needful to circumcise them:
the Gentiles that believed:

and to command them to keep the law of Moses;
both moral and ceremonial; the observance of which they reckoned was absolutely necessary to salvation. Some think these are not the words of Luke, relating what happened at Jerusalem, when Paul and Barnabas gave in their account of things to the apostles and elders; but that they are a continuation of their account, how that in the controversy raised at Antioch, certain Pharisees that came thither from Judea, rose up and asserted the necessity of the, Gentiles being circumcised, and of their keeping the law of Moses in order to their being saved; which is favoured by the Syriac version, especially by the Latin interpreter of it, who supplies the words thus, "but say they" (i.e. Paul and Barnabas) "there arose men"