This is referring back to the group mentioned in verse 1 this was why Paul went to Jerusalem. They were teaching them to keep the law for salvation. The group spoken about in verse 5 was already present in Jerusalem. It’s a different group that was never spoken against in the entire passage. Also notice the group in verse one are not said to be Pharisees.
This is getting off topic so feel free to split this off if you think it best.
I know that the idea of keeping the law runs counter to mainstream teaching and therefore the default assumption is that those in verse 5 were false brethren but that’s not what the passage actually teaches. Paul never stopped being a Pharisee he testifies later in a court of law that he is (present tense) a Pharisee, also he never converted to anything. The footnotes in your bible are not inspired.
In Acts 21:24,25 Paul is basically coerced to outwardly perform the completion phase of a vow with some other men who have made a vow to disprove that he is not anti Torah, and that he walkest orderly, and keeps the law.
“As touching the Gentiles which believe, (post conversion) we have written and concluded that they observe no such thing (the law) save only that they keep themselves from things offered to idols, and from blood, and from strangled, and from fornication.
At best, following the law post conversion is a Jewish injunction. There is no imperative to do so (per the apostles) unless you are Jewish and even that is arguable under the new covenant where there is now no distinction between Jew or Greek, bond or free, male or female but we are all one in Christ.
Acts 21:24,25 is a reference back to the Acts 15 conference that Paul is referring to in Galatians 2. (I looked for another conference that was even close to these parameters and couldn’t find one even close). To say that the only issue refuted in Acts 15 is a pre conversion issue, rather than a pre and post conversion issue, is to ignore that the men who had come to Antioch were attempting to coerce
Believers into circumcision, not prospective believers. Paul makes clear that these men were attacking believers on both fronts, pre and post conversion in Galatians 3:3. Are ye so foolish? Having begun in the Spirit (conversion), are ye now (post conversion) made perfect by the flesh?
These psuedo brethren were also attempting to ostracise Gentile Believers who weren’t Torah observant based on a Torah principle found in Exodus 34:15. This is the same principle that Peter wrestled with personally in chapter 10 and was bludgeoned about the head and shoulders with in Chapter 11:2,3 by those of the circumcision. They didnt back off until Peter used the “God told me too” trump card for their legitimate Torah objections.
It also ignores that both sides of the argument in Antioch go to Jerusalem to ask
this question of the apostles and elders. “When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas,
and certain other of them, should go up to Jerusalem . . .”
Verse 4 is Paul and Barnabas presenting their side of the argument, and verse 5 is the other side presenting their arguments. Whether or not the exact Pharisees presenting the argument were the same exact men who were creating dissection in Antioch, or whether they were deferring the presentation to others of the circumcision (that sent them out) is irrelevant. They were all of the same persuasion and prosecuted the same charge(s).
IMO, These are the same “certain men” of verse one that come to Antioch, the same “certain other of them” from verse 2 that return to Jerusalem. The same “certain of the sect of Pharisees” in verse 5 that present the prosecution, and the same “certain which went out from us that have troubled you, subverting your souls” in verse 24.
The sentence given is the same recorded in Acts 21 passage as well as in the letter sent to the churches that state: Forasmuch as we have heard that certain which went out from us have troubled you with words, subverting your souls, saying, Ye must be (1) circumcised and (2)keep the law: to whom we gave no such commandment:
The proscription for Gentiles to keep the Mosaic law is counter to apostolic instruction.
As to Paul extolling his Pharisee credentials, there are two places where Paul does this. Once in the legal challenge, but this was only done to divide the multitude that was arrayed against him, not to necessarily align himself with Torah. Acts 23:6&7. A bit misleading to try to use this example to prove Torah observant. Paul used this pedigree to his advantage, just as he often used his Roman citizenship.
The second is in Philippians 3:5-8 and is an account of his history and pedigree. His past (unless he needed to divide and conquer). But what things were gain to me, those I counted loss for Christ. . . .. 8 for whom I have suffered the loss of all things, and do count them but dung, that I may win Christ. (His status as blameless in the righteousness of the law is also included in the dung category)
