Nicene and Post-Nicene Fathers, Vol. III:
Moral Treatises of St. Augustin: Section 28

28. Therefore, if we compare the things themselves, we may no way doubt that the chastity of continence is better than marriage chastity, whilst yet both are good: but when we compare the persons, he is better, who hath a greater good than another. Further, he who hath a greater of the same kind, hath also that which is less; but he, who only hath what is less, assuredly hath not that which is greater. For in sixty, thirty also are contained, not sixty also in thirty. But not to work from out that which he hath, stands in the allotment of duties, not in the want of virtues: forasmuch as neither is he without the good of mercy, who finds not wretched persons such as he may mercifully assist.