Galatians 5:3

For I testify again. — Translate rather, Nay, I protest again, introducing a further argument. He who allows himself to be circumcised thereby commits himself wholly to the Law, just as, it might be said, he who is baptised commits himself wholly to Christ. The act of circumcision placed a man under the legal system, just as the act of baptism placed him under the Christian system. From that time forward he could not choose one part and refuse another, but was bound alike by all.

He is a debtor. — He is under an obligation.