Commentary on the Epistle to the Galatians. Martin Luther

Titus for the reason that the false apostles wanted to compel him to circumcise Titus. Paul refused to accede to their demands. If they had asked it on the plea of brotherly love, Paul would not have denied them. But because they demanded it on the ground that it was necessary for salvation, Paul defied them, and prevailed. Titus was not circumcised.