3 “But what kind of sin had these children,” it may be said, “that they should do it away? For touching those who are of full age, and have been guilty of many negligences, one might with show of reason speak thus: but they who so underwent premature death, what sort of sins did they by their sufferings put away?” Did you not hear me say, that though there were no sins, there is a recompense of rewards hereafter for them that suffer ill here? Wherein then were the young children hurt in being slain for such a cause, and borne away speedily into that waveless harbor? “Because,” do you say, “they would in many instances have achieved, had they lived, many and great deeds of goodness.” Why, for this cause He lays up for them beforehand no small reward, the ending their lives for such a cause. Besides, if the children were to have been any great persons, He would not have suffered them to be snatched away beforehand. For if they that eventually will live in continual wickedness are endured by Him with so great long-sufferings, much more would He not have suffered these to be so taken off had He foreknown they would accomplish any great things.
And these are the reasons we have to give; yet these are not all; but there are also others more mysterious than these, which He knows perfectly, who Himself orders these things. Let us then give up unto Him the more perfect understanding of this matter, and apply ourselves to what follows, and in the calamities of others let us learn to bear all things nobly. Yea, for it was no little scene of woe, which then befell Bethlehem, the children were snatched from their mother's breast, and dragged unto this unjust slaughter.
And if you are yet faint-hearted, and not equal to controlling yourself in these things, learn the end of him who dared all this, and recover yourself a little. For very quickly was he overtaken by punishment for these things; and he paid the due penalty of such an abominable act, ending his life by a grievous death, and more pitiable than that which he now dared inflict; suffering also countless additional ills, which you may know of by perusing Josephus' account of these events. But, lest we should make our discourse long, and interrupt its continuity, we have not thought it necessary to insert that account in what we are saying.
Source: Homilies on the Gospel of St. Matthew (New Advent)