2 Corinthians 10:1

Therefore I exhort you, brothers, by the mercies of God, to present your bodies as a sacrifice—living, holy, and pleasing to God, which is your spiritual service of worship.

since you are seeking proof that Christ speaks in me; He is not weak toward you, but mighty in you.

Behold I, Paul, say to you that if you receive circumcision, Christ will be of no benefit to you.

I, Paul, am writing this with my own hand, I will repay it (not to mention to you that you owe to me even your own self as well).

Paul Defends His Authority