77 But we need not be moved by this circumstance. For who would venture to affirm, in regard to those white-robed saints, when they pleaded that they should be avenged, whether they pleaded against the men themselves or against the dominion of sin? For of itself it is a genuine avenging of the martyrs, and one full of righteousness and mercy, that the dominion of sin should be overthrown, under which dominion they were subjected to so great sufferings. And for its overthrow the apostle strives, saying, “Let not sin therefore reign in your mortal body.” But the dominion of sin is destroyed and overthrown, partly by the amendment of men, so that the flesh is brought under subjection to the spirit; partly by the condemnation of those who persevere in sin, so that they are righteously disposed of in such a way that they cannot be troublesome to the righteous who reign with Christ.
Look at the Apostle Paul; does it not seem to you that he avenges the martyr Stephen in his own person, when he says: “So fight I, not as one that beats the air: but I keep under my body, and bring it into subjection”? For he was certainly laying prostrate, and weakening, and bringing into subjection, and regulating that principle in himself whence he had persecuted Stephen and the other Christians. Who then can demonstrate that the holy martyrs were not asking from the Lord such an avenging of themselves, when at the same time, in order to their being avenged, they might lawfully wish for the end of this world, in which they had endured such martyrdoms?
And they who pray for this, on the one hand pray for their enemies who are curable, and on the other hand do not pray against those who have chosen to be incurable: because God also, in punishing them, is not a malevolent Torturer, but a most righteous Disposer. Without any hesitation, therefore, let us love our enemies, let us do good to those that hate us, and let us pray for those who persecute us.
Source: Our Lord's Sermon on the Mount (New Advent)