What does 2 Corinthians 3:5 mean?

In the previous verse, Paul referred to the absolute confidence he has that his ministry of representing Christ is from God. Now he makes clear that his is not a confidence built on belief in himself or his own skills, abilities, and knowledge.

At one time, Paul would likely have placed great confidence in himself based on those things. He wrote this in Philippians 3:4–6, "If anyone else thinks he has reason for confidence in the flesh, I have more: circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as to the law, a Pharisee; as to zeal, a persecutor of the church; as to righteousness under the law, blameless."

But when he came to Christ, Paul lost all that earthly, religious confidence, "But whatever gain I had, I counted as loss for the sake of Christ" (Philippians 3:7). Now he writes that any selfish version of self-confidence is gone. He does not believe he and his co-workers are sufficient in themselves to take any credit. They are not ultimately responsible for delivering anything of value to the Corinthians. Instead, their sufficiency comes from God. It is by God's power they deliver God's message to the people God wants to reach.