Paul defends himself through logic. If he preached what they demanded, there would be no cost. But there is a cost. The offense of the cross is real. And he is still bearing it. Meditate on the word offense. What it means that the cross carries one.
Galatians 5: 11
But if I, brothers, still preach circumcision, why am I still being persecuted? In that case the offense of the cross has been removed.