“As the truth of Christ is in me…” (II Cor. 11:10).
Look how often Paul, in his letters, speaks with an oath: “God is my witness” (Rom. 1:9), “As God is true” (II Cor. 1:18), “Behold, before God, I lie not” (Gal. 1:20), “God is my record” (Phil. 1:8), “I speak the truth in Christ, and lie not” (I Tim. 2:7), etc., etc.
As Dean Howson has said: “When Paul makes a solemn statement under the sense of God’s presence, he does not hesitate to express this.”
But had not others spoken under the sense of God’s presence? Of course they had, yet Paul calls God to witness far more often than any other Bible writer. Why is this? The answer is found in the distinctive character of Paul’s ministry as the apostle of “the mystery.” John the Baptist, the four evangelists and the twelve apostles did not need to speak with oaths since they proclaimed that which had already been prophesied. But with Paul it was different. Separate from the twelve, who were widely known as the apostles of Christ, Paul had been raised up to make known a wonderful secret which God had kept hidden from all who had gone before. While not a contradiction of prophecy, this secret had nevertheless not been prophesied; it was a new revelation. Hence it was appropriate that the Apostle should insist again and again that he wrote as in the presence of God.
As we consider Paul’s oaths, however, we must ask ourselves whether anyone ever used the oath with more solemn sincerity. Did anyone ever suffer so intensely for the truths he proclaimed, or pay so dearly to convince others of them? Could anyone say with such simplicity to those who knew him best:
“Ye know… after what manner I have been with you at all seasons, serving the Lord with all humility of mind, and with many tears and temptations [testings]… and how I kept back nothing that was profitable unto you…” (Acts 20:18-20). source