John Calvin Commentary Galatians 1:20

"Now touching the things which I write unto you, behold, before God, I lie not." — Galatians 1:20 (ASV)

Now the things which I write to you. This affirmation extends to the whole narrative.

The vast earnestness of Paul on this subject is shown by his resorting to an oath, which can only lawfully be used on great and weighty occasions. It is no wonder that he insists with so much earnestness on this point, for we have already seen what tactics the impostors resorted to in order to take away his name and credibility as an apostle.

Now, the ways of swearing used by good men deserve our attention, for we learn from them that an oath must be viewed simply as an appeal to the judgment-seat of God for the integrity and truth of our words and actions; and such a transaction should be guided by religion and the fear of God.