So great had been his desire to be approved and supported by those whom you wish on all occasions to be understood as in alliance with Judaism! When indeed he says, that "neither was Titus circumcised," he for the first time shows us that circumcision was the only question connected with the maintenance of the law, which had been as yet agitated by those whom he therefore calls "false brethren unawares brought in.
When he first says, "Neither Titus, who was with me, being a Greek, was compelled to be circumcised," and then adds, "And that because of false brethren unawares brought in," etc.
The implication is “Why should you be circumcised, when Titus was not compelled to undergo circumcision by the apostles? Titus, who had an important role, was accepted without circumcision.”
Ver. 3. "But not even Titus, who was with me, being a Greek, was compelled to be circumcised."
What means, "being a Greek?" Of Greek extraction, and not circumcised; for not only did I so preach but Titus so acted, nor did the Apostles compel him to be circumcised. A plain proof this that the Apostles did not condemn Paul's doctrine or his practice. Nay more, even the urgent representations of the adverse party, who were aware of these facts, did not oblige the Apostles to enjoin circumcision, as appears by his own words —
(Vers. 3-5.) But not even Titus, who was with me, though he was a Gentile, was compelled to be circumcised. Yet because of false brothers secretly brought in—who slipped in to spy out our freedom that we have in Christ Jesus, so that they might bring us into slavery— to them we did not yield in submission even for a moment, so that the truth of the gospel might be preserved for you. But even Titus, who was with me, was not compelled to be circumcised, although he was a Gentile. This matter arose because of false brothers secretly brought in, who slipped in to spy out our freedom that we have in Christ Jesus, so that they might bring us into slavery. But what is this truth of the Gospel, to give in to the hypocrisy of the Jews; and to consider as scybala what you once esteemed, and to despise as losses, and to observe and esteem as something, when they are nothing? But it strongly opposes the meaning of the Epistle itself, to call the Galatians back to circumcision. This is the main theme throughout his discourse, to teach that he is a Hebrew among the Hebrews, once observing all the works of the Law, circumcised on the eighth day according to the Law of the Pharisees: nevertheless, for the grace of Christ, to completely despise everything. For when he went to Jerusalem, and the false brethren, who believed in circumcision, wanted to compel him to circumcise Titus; neither Titus, nor did he give in to violence, so that they would safeguard the truth of the Gospel. But if he says that he was compelled by necessity to circumcise Titus: how does he recall the Galatians from circumcision, from which neither Titus, who was with him from the Gentiles, could excuse himself in Jerusalem? Therefore, according to the Greek manuscripts, it should be read, 'To whom we did not yield in subjection, not even for an hour,' so that it may be understood subsequently: so that the truth of the Gospel may remain with you. But if the testimony of the Latin exemplars is pleasing to anyone, we must understand it according to the higher sense: that the purpose was not for Titus to be circumcised, but to go to Jerusalem. For this reason, Paul and Barnabas submitted to going to Jerusalem, due to the sedition caused by the Law of Antioch. This was done so that the truth of the Gospel would be confirmed by the letter of the apostles and remain among the Galatians, which was not in the literal sense, but in the spiritual sense. It was not in the carnal understanding, but in spiritual intelligence, and not in overt Judaism, but in hidden understanding. It is worth knowing that the conjunction 'autem,' which is placed in this position, is superfluous if it is read without any purpose to respond to it and if it concludes the previous statement. However, it serves to maintain the order of reading and the sense of the passage. So, Titus, who was with me, being a Gentile, was not compelled to be circumcised. And immediately after, it explains the reason why he was being urged to undergo circumcision against his will. 'Because of the false brothers secretly brought in, who slipped in to spy out our freedom that we have in Christ Jesus, so that they might bring us into slavery.' But when they were serving as ministers and wished to drag us into the servitude of the Law from the freedom of Christ, we did not even yield to them for a moment, so that we might not give any occasion to them to accuse us. And we did this primarily because of the ecclesiastical peace, so that we could excuse ourselves from necessity, and we did all of this so that you would not have any opportunity to depart from the grace of the Gospel. Therefore, if we, while in Jerusalem, among so many Jews who were falsely claiming to be brothers and those who were exerting influence over us to some extent, could not be compelled by force or reason to observe the circumcision that we knew was abolished, then you, coming from the Gentiles, you in Galatia, you to whom no violence can be done, voluntarily abandoning the grace, have transcended the antiquity of the already abolished Law.
It was because of the intrigues of false brethren that Titus was not compelled to be circumcised. It was not possible to require circumcision of him. Those who had crept in to spy on their liberty had a vehement expectation and desire for the circumcision of Titus. They wanted, with Paul’s testimony and consent, to preach circumcision as necessary to salvation.
That is, by the Apostles; which is, of course, a highest proof that they should not pass sentence against the Apostle, who did not circumcise the nations.
[AD 220] Tertullian on Galatians 2:3