John Chrysostom

And he said, Who art Thou Lord? thus in the first place confessing himself His servant. And the Lord said, I am Jesus, whom thou persecutest: think not thy warring is with men.

Homily on Acts 19 ↗

Theophylact of Ohrid

"I am Jesus, whom you persecute." This is said instead of "do not think that you are warring against men, but against Me, your Lord." Why was this appearance and admonition to Saul not made at the beginning? In order to show that Christ truly rose from the dead. For how would the persecutor of Him, who did not believe in His resurrection and was furiously pursuing the believers, have come to faith if the power of His resurrection were not great? And why not immediately after the resurrection? …

Commentary on Acts ↗

Cyprian

For consider what glory it is to set aside the lusts of this life, and to oppose a mind withdrawn from all commerce with nature and the world, to all the opposition of the adversary, and to have no dread of the cruelty of the torturer; that a man should be animated by the suffering whereby he might be believed to be destroyed, and should take to himself, as an enhancement of his strength, that which the punisher thinks will aggravate his torments. …

Pseudo-Cyprian On the Glory of Martyrdom ↗

Bede

I am Jesus, whom you are persecuting. He did not say: I am God, I am the Son of God, but he says: Accept the weakness of my humility and lay down the scales of your pride.

Commentary on Acts ↗