Of God and His Creatures

Celibacy can be justified on mere natural and rational grounds in this sense, that no cogent reasons are apparent making it a man's duty under ordinary circumstances to marry. But celibacy does not amount to a virtue except when it is embraced on supernatural grounds, that is to say, on grounds of faith and love of God in Christ.

The chapter next translated is the justification of the vow of obedience.

Of God and His Creatures: 3.137