Галатам 1:20

Solemn asseveration that his statement is true that his visit was but for fifteen days and that he saw no apostle save Peter and James. Probably it had been reported by Judaizers that he had received a long course of instruction from the apostles in Jerusalem from the first; hence his earnestness in asserting the contrary facts.

In this chapter, after the preface or introduction (Gal 1:1-5), the apostle severely reproves these churches for their defection from the faith (Gal 1:6-9), and then proves his own apostleship, which his enemies had brought them to question, I. From his end and design in preaching the gospel (Gal 1:10). II. From his having received it by immediate revelation (Gal 1:11, Gal 1:12). For the proof of which he acquaints them, 1. What his former conversation was (Gal 1:13, Gal 1:14). 2. How he was converted, and called to the apostleship (Gal 1:15, Gal 1:16). 3. How he behaved himself afterwards (Gal 1:16 to the end).

1:20 I declare before God: Paul here takes an oath to emphasize the truthfulness of his account of his trip to Jerusalem.