The saint's response: "So that my eyes might be pure when I one day behold the Blessed Mother."
Incidentally, here is a good custom for men who try to keep their eyes and hearts pure. I have memorized the following Bible verse and I recite it when I am tempted by the eyes:
"I have made a covenant with my eyes, that I would not so much as look upon a virgin" (Job 31:1).
It's very effective and it's also worthy invoking the Dominican St Thomas Aquinas who is said to have been one of the purest men ever to live.
My suspicion is that Thomas Aquinas was gifted with so much intelligence and knowledge since he practiced a perfect mortification of the passions. When the flesh is tempered, the mind is truly free to perceive profound mysteries.
St Dominic and St Thomas, pray for us.