23. So then, my brethren, give heed. Those famous men who marry wives only for the procreation of children, such as we read the Patriarchs to have been, and know it, by many proofs, by the clear and unequivocal testimony of the sacred books; whoever, I say, they are who marry wives for this purpose only, if the means could be given them of having children without intercourse with their wives, would they not with joy unspeakable embrace so great a blessing? would they not with great delight accept it? For there are two carnal operations by which mankind is preserved, to both of which the wise and holy descend as matter of duty, but the unwise rush headlong into them through lust; and these are very different things. Now what are these two things by which mankind is preserved? The first which is confined to ourselves and relates to taking nourishment (which cannot of course be taken without some gratification of the flesh), is eating and drinking; if you do not this you will die. By this one support then of eating and drinking does the race of man subsist, by a law of its nature. But by this men are only supported as far as themselves are concerned; for they do not provide for any succession by eating and drinking, but by marrying wives. For so is the race of man preserved; first, by the means of life; but because whatever care they exercise they cannot of course live for ever, there is a second provision made, that those who are newly born may replace those who die. For the race of man is, as it is written, like the leaves on a tree, or an olive, that is, or a laurel, or some tree of this sort, which is never without foliage, yet whose leaves are not always the same. For, as it is written, “it shooteth forth some, and casteth others,” because those which sprout afresh replace the others as they fall, for the tree is ever casting its leaves, yet is ever clothed with leaves. So also the race of man feels not the loss of those who die day by day, because of the supply of those who are newly born; and thus the whole race of mankind is according to its own laws sustained, and as leaves are ever seen on the trees, so is the earth seen to be full of men. Whereas if they were only to die, and no fresh ones be born, the earth would be stripped of all its inhabitants, as certain trees are of all their leaves.