Verse 20. Behold, before God, I lie not. This is an oath, or a solemn appeal to God. See Note, Ro 9:1. The design of this oath here is to prevent all suspicion of falsehood. It may seem to be remarkable that Paul should make this solemn appeal to God in this argument, and in the narrative of a plain fact, when his statement could hardly be called in question by any one. But we may remark,

(1.) that the oath here refers not only to the fact that he was with Peter and James but fifteen days, but to the entire group of facts to which he had referred in this chapter. "The things which I write unto you." It included, therefore, the narrative about his conversion, and the direct revelation which he had from the Lord Jesus.

(2.) There were no witnesses which he could appeal to in this case, and he could therefore only appeal to God. It was probably not practicable for him to appeal to Peter or James, as neither of them were in Galatia, and a considerable part of the transactions here referred to occurred where there were no witnesses. It pertained to the direct revelation of truth from the Lord Jesus. The only way, therefore, was for Paul to appeal directly to God for the truth of what he said.

(3.) The importance of the truth here affirmed was such as to justify this solemn appeal to God. It was an extraordinary and miraculous revelation of the truth by Jesus Christ himself. He received information of the truth of Christianity from no human being. He had consulted no one in regard to its nature. That fact was so extraordinary, and it was so remarkable that the system thus communicated to him should harmonize so entirely with that taught by the other apostles with whom he had had no intercourse, that it was not improper to appeal to God in this solemn manner. It was, therefore, no trifling matter in which Paul appealed to God; and a solemn appeal of the same nature, and in the same circumstances, can never be improper.