Jamieson, Fausset and Brown on Galatians 1:16

16. reveal his Son in me--within me, in my inmost soul, by the Holy Spirit (Ga 2:20). Compare 2Co 4:6, "shined in our hearts." The revealing of His Son by me to the Gentiles (so translate for "heathen") was impossible, unless He had first revealed His Son in me; at first on my conversion, but especially at the subsequent revelation from Jesus Christ (Ga 1:12), whereby I learned the Gospel's independence of the Mosaic law.

that I might preach--the present in the Greek, which includes the idea "that I may preach Him," implying an office still continuing. This was the main commission entrusted to him (Ga 2:7, 9).

immediately--connected chiefly with "I went into Arabia" (Ga 1:17). It denotes the sudden fitness of the apostle. So Ac 9:20, "Straightway he preached Christ in the synagogue."

I conferred not--Greek, "I had not further (namely, in addition to revelation) recourse to ... for the purpose of consulting." The divine revelation was sufficient for me [Bengel].

flesh and blood--(Mt 16:17).