Gal 6:14-15
"Far be it from me to boast except in the cross of our Lord Jesus Christ, by which the world has been crucified to me, and I to the world. For neither circumcision counts for anything, nor uncircumcision, but a new creation."
The conclusion of the entire letter: the cross is the only foundation for boasting. Not circumcision, not works of the law, not ministerial success. The cross has crucified the world to Paul and Paul to the world — a radical separation from all worldly value systems. The new creation (kaine ktisis) is what matters.