Charles Ellicott Commentary Galatians 5:3

"Yea, I testify again to every man that receiveth circumcision, that he is a debtor to do the whole law." — Galatians 5:3 (ASV)

For I testify again.—Translate rather, No, 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 baptized 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.