John Calvin Commentary Galatians 2:3

"But not even Titus who was with me, being a Greek, was compelled to be circumcised:" — Galatians 2:3 (ASV)

But neither Titus. This is an additional argument to prove that the Apostles held the same views as he did; for he had brought to them an uncircumcised man, whom they did not hesitate to acknowledge as a brother. The reason why he was not circumcised is explained: for circumcision, being a matter of indifference, might be neglected or practiced as edification required.

Our invariable rule of action is that if all things are lawful for us (1 Corinthians 10:23), we ought to inquire what is expedient. He circumcised Timothy (Acts 16:3) in order to take away a ground of offense from weak minds, for he was at that time dealing with weak minds, which it was his duty to treat with tenderness. And he would gladly have done the same thing with Titus, for he was tireless in his efforts to support the weak (Acts 20:35); but the case was different.

For some false brethren were watching for an opportunity to slander his doctrine and would immediately have spread the report: “See how the valiant champion of liberty, when he comes into the presence of the apostles, lays aside the bold and fierce aspect which he is accustomed to assume among the ignorant!”

Now, as it is our duty to bear the infirmities of the weak (Romans 15:1), so concealed foes, who deliberately lie in wait for our liberty, must be vigorously resisted. The duties of love to our neighbor ought never to be injurious to faith; and therefore, in matters of indifference, the love of our neighbor will be our best guide, provided that faith always receives our first regard.