19 And if ever, while you have been sitting here, a thought concerning chastity or virginity has come into your mind, it has been His teaching. Has not often a maiden, already at the bridal threshold, fled away, He teaching her the doctrine of virginity? Has not often a man distinguished at court, scorned wealth and rank, under the teaching of the Holy Ghost? Has not often a young man, at the sight of beauty, closed his eyes, and fled from the sight, and escaped the defilement?
Askest thou whence this has come to pass? The Holy Ghost taught the soul of the young man. Many ways of covetousness are there in the world; yet Christians refuse possessions: wherefore? Because of the teaching of the Holy Ghost. Worthy of honour is in truth that Spirit, holy and good; and fittingly are we baptized into Father, Son, and Holy Ghost. A man, still clothed with a body, wrestles with many fiercest demons; and often the demon, whom many men could not master with iron bands, has been mastered by the man himself with words of prayer, through the power which is in him of the Holy Ghost; and the mere breathing of the Exorcist becomes as fire to that unseen foe.
A mighty ally and protector, therefore, have we from God; a great Teacher of the Church, a mighty Champion on our behalf. Let us not be afraid of the demons, nor of the devil; for mightier is He who fights for us. Only let us open to Him our doors; for He goes about seeking such as are worthy and searching on whom He may confer His gifts.
Source: Catechetical Lectures (New Advent)