However, it is right not to overlook what a little before came into my recollection, and was brought forward for a testimony. And what then was this? We were speaking of the Jews, and of the chief rulers among them, how that they were blamed, as seeking retaliation. And yet this the law permitted them; “eye for eye, and tooth for tooth.” True, but not to the intent that men should pluck out each other's eyes, but that they should check boldness in aggression, by fear of suffering in return, and thus should neither do any evil to others, nor suffer any evil from others themselves. Therefore it was said, “eye for eye,” to bind the hands of the aggressor, not to let yours loose against him; not to ward off the hurt from your eyes only, but also to preserve his eyes safe and sound.
But, as to what I was enquiring about—why, if retaliation was allowed, were they arraigned who practiced it? Whatever can this mean? He here speaks of vindictiveness; for on the spur of the moment he allows the sufferer to act, as I was saying, in order to check the aggressor; but to bear a grudge he permits no longer; because the act then is no longer one of passion, nor of boiling rage, but of malice premeditated. Now God forgives those who may be carried away, perhaps upon a sense of outrage, and rush out to resent it. Hence He says, “eye for eye”; and yet again, “the ways of the revengeful lead to death.” Now, if, where it was permitted to put out eye for eye, so great a punishment is reserved for the revengeful, how much more for those who are bidden even to expose themselves to ill-treatment. Let us not then be revengeful, but let us quench our anger, that we may be counted worthy of the lovingkindness, which comes from God (“for with what measure,” says Christ, “ye mete, it shall be measured unto you, and with what judgment ye judge, you shall be judged”), and that we may both escape the snares of this present life, and in the day that is at hand, may obtain pardon at His hands, through the grace and loving-kindness of our Lord Jesus Christ, with whom, to the Father, together with the Holy Ghost, be glory, power, honor, both now and forever and ever. Amen.
Source: Homilies on Ephesians (New Advent)