Albert Barnes on Acts 26:19

Whereupon. Whence, οθεν. Since the proof of his being the Messiah, and of his resurrection, and of his calling me to this work, was so clear and plain, I deemed it my duty to engage without delay in the work.

I was not disobedient. I was not incredulous or unbelieving; I yielded myself to the command, and at once obeyed. See Acts 9:6; Comp. Gall 1:16.

To the heavenly vision. To the celestial appearance; or to the vision which appeared to me manifestly from heaven. I did not doubt that this splendid appearance Acts 26:13 was from heaven; and I did not refuse to obey the command of Him who thus appeared to me. He knew it was the command of God his Saviour; and he gave evidence of repentance by yielding obedience to it at once.