39 For this cause therefore that light which was overpowering, because it was not diminished, entered the eyeballs with overpowering manifestation and injured them. But the Lord of the light, because He had lowered Himself in order to help, His lowly voice entered the ears that had need and helped them. But in order that the help of that voice which had become lowly, might not fail Him, therefore the strength of that light was not lowered, in order that because of that light, which was not lowered, the help of that voice which was lowered, might be believed.
But this is a marvel, that until our Lord made Himself lowly in voice, Paul was not made lowly in deed; for even as, before He came down and clothed Himself in a body, our Lord was in exaltation with His Father; yet in His exaltation men did not learn humility; but when He humbled Himself and came down from His exaltation, then by His humbleness humility was soon among men; so again after His resurrection and ascension He was in glory at the right hand of God His Father, but by that His exaltation, Paul did not learn humility.
Therefore He that was exalted and sat at the right hand of His Father, ceased from glorious and lofty speech, and He cried as one wronged and oppressed, with feeble and meek words, saying— Saul, Saul, why do you persecute Me? Thus, humble words prevailed over harsh bridles. For by humble words, as by bridles, the persecuted led the persecutor from the broad way of the persecutors into the narrow way of the persecuted. And since all the signs that were done in the Name of our Lord did not convince Paul, our Lord made haste to meet with humility him who was hastening on the way to Damascus in the vehemence of pride. Thus by His humble words, the harsh vehemence of pride was checked.
Source: On Our Lord (New Advent)