The first question is whether “men of the circumcision” is used to include all Jews or whether it referred to some sub-set of Jews.
10 Aristarchus my fellow prisoner greets you, and Mark the cousin of Barnabas (concerning whom you have received instructions—if he comes to you, welcome him), 11 and Jesus who is called Justus. These are the only men of the circumcision among my fellow workers for the kingdom of God, and they have been a comfort to me. 12 Epaphras, who is one of you, a servant of Christ Jesus, greets you, always struggling on your behalf in his prayers, that you may stand mature and fully assured in all the will of God. 13 For I bear him witness that he has worked hard for you and for those in Laodicea and in Hierapolis. 14 Luke the beloved physician greets you, as does Demas. Colossians 4:10–14 (ESV).
These three (Aristarchus, Mark, and Jesus Justus), or perhaps just the latter two (the inclusion of Aristarchus in Acts 20:4 may point to his being a Gentile; so Dibelius, Kolosser, Epheser, Philemon 51), are together described as “the ones who are from circumcision” (οἱ ὄντες ἐκ περιτομῆς). Similar phrases occur elsewhere in the Pauline corpus with a hint of menace or at least of hostility (Gal. 2:12; Tit. 1:10). Here it may simply denote Jews, the people marked out by the distinguishing feature of circumcision (see on 2:11), but probably with the hint that “those of the circumcision” were usually active in hostility to Paul’s mission.10 The reference presumably is intended to assure the Colossians that there were such Jews, or at any rate other Jews apart from himself, who, as Jews, were fully approving of and cooperative in the Gentile mission (“fellow workers”), despite, presumably, the disapproval of most of their compatriots (cf. Ollrog 45–46). This point is obscured by those who translate “Jewish Christians” (NEB/REB) or “Jewish converts” (GNB), which suggests that it was something more than their Jewishness which qualified them for mention here (but Paul does not say οἱ ὄντες ἐκ περιτομῆς ἐν Χριστῷ). Rather, it is precisely that they can be described as οἱ ὄντες ἐκ περιτομῆς pure and simple which gives the reference its significance.
That the reference is thus made strengthens the likelihood that any threats to the Colossian church’s self-understanding came from the Colossian synagogue; why otherwise such a full reference added to them, when the notes added to Luke and Demas (equally “coworkers” in Phm. 24) are so brief (4:14)? And why mention these individuals, less well known to the Colossians, before he mentions their own Epaphras (4:12; contrast Phm. 23–24), unless he wanted to give particular prominence to them precisely because they were Jews? Furthermore, that the reference is made without any sign of resentment or hostility to “the circumcision” (contrast Gal. 2:12 and Tit. 1:10) equally strengthens the suggestion that the threat from the Colossian synagogue was not at all so forceful as earlier in Galatia, nor was it making such an issue of circumcision as there.
There is a qualification, however. The writer adds: “these alone fellow workers for the kingdom of God” — that is, “these are the only Jews among my fellow workers for the kingdom of God” (NIV). The qualification is not very extensive: it refers only to Paul’s “fellow workers” (there were many other Jews who had confessed Jesus as Lord), and since his circle of “coworkers” at previous and other times certainly included other Jews (e.g., Priscilla and Aquila, Timothy and Silvanus: Rom. 16:3, 21; 2 Cor. 1:24),11 the reference here must be to those presently with him. In fact the immediate circle does not seem to have been very large (six names in 4:10–14), so that the note of evident sadness (“these only”) is all the more striking. It underlines the extent to which Paul was (or was perceived by his immediate circle to be) deeply concerned about the relative failure of his people to accept the gospel of Jesus Christ, and probably still more about the seemingly negative effect of the success of his Gentile mission on his fellow Jews — an echo of old disputes of which we still have record (Gal. 2:11–18; 5:1–12; 6:12–14; 2 Cor. 11:1–23; Phil. 3:2–21). That he could so express himself, without yielding the point that the gospel was as fully for Gentiles as Gentiles as for Jews as Jews, is a reminder of the complexity of Paul’s personal involvement in the whole business. Presumably something at least of all this is in mind in the fact that it is just these fellow Jews who are described as having been or become such a “comfort” (παρηγορία, only here in the New Testament; see BAGD; MM; Lohse 173 n. 29) to Paul.
James D. G. Dunn, The Epistles to the Colossians and to Philemon : A Commentary on the Greek Text (Grand Rapids, Mich.; Carlisle: William B. Eerdmans Publishing; Paternoster Press, 1996), 278-80.