24 Marriage, I say, is a good, and may be, by sound reason, defended against all calumnies. But with the marriage of the holy fathers, I inquire not what marriage, but what continence, is on a level: or rather not marriage with marriage; for it is an equal gift in all cases given to the mortal nature of men; but men who use marriage, forasmuch as I find not, to compare with other men who used marriage in a far other spirit, we must require what continent persons admit of being compared with those married persons. Unless, haply, Abraham could not contain from marriage, for the sake of the kingdom of heaven, he who, for the sake of the kingdom of heaven, could fearless sacrifice his only pledge of offspring, for whose sake marriage was dear!
Source: On the Good of Marriage (New Advent)