“Pray for those who persecute you: Christ did not simply command to love but to pray. Do you see how many steps he has ascended and how he has set us on the very summit of virtue? Mark it, numbering from the beginning. A first step is not to begin with injustice. A second, after one has begun, is not to vindicate oneself by retaliating in kind. A third, to refuse to respond in kind to the one who is injuring us but to remain tranquil. A fourth, even to offer up one’s self to suffer wrongfully. A fifth, to give up even more than the wrongdoer wishes to take. A sixth, to refuse to hate one who has wronged us. A seventh, even to love such a one. An eighth, even to do good to that one. A ninth, to entreat God himself on our enemy’s behalf. Do you perceive how elevated is a Christian disposition? Hence its reward is also glorious. Chrysostom. The Gospel of Matthew, Homily 18.4"
“The perfection of loving the enemy: He who loves his friends loves them for his own sake, not on account of God, and therefore he has no treasure. The loving itself delights him. However, he who loves his enemy loves not for his own sake but on account of God. Hence he has great treasure, because he goes against his own instincts. For where labor sows the seed, there it reaps the fruit. “Be ye therefore perfect, just as your Father is perfect.” He who loves his friend does not in fact sin but does not work justice. It is half a good that one depart from evil and not pursue good. It is perfect, however, that one not only flee evil but also accomplish good. So he said, “be perfect,” so that you might both love your friends on account of shunning evil and love your enemies on account of possessing justice. The formerfrees us from punishment; the latter leads us into glory. For a representative of God is not perfect who does not resemble God through his or her works. Anonymous. Incomplete Work on Matthew, Homily 13"
“All things are perfected by goodness: The law used to demand that your neighbor be loved and allowed hatred against an enemy. Faith, rather, requires that enemies be cherished. It breaks the tendency we have to be peevish and urges us to bear life’s difficulties calmly. Faith not only deters anger from turning into revenge but even softens it into love for the injurer. It is merely human to love those who love you, and it is common to cherish those who cherish you. Therefore Christ calls us into the life of heirs of God and to be models for the just and the unjust of the imitation of Christ. He distributes the sun and the rain through his coming in baptism and by the sacraments of the Spirit. Thus he has prepared us for the perfect life through this concord of public goodness, because we must imitate our perfect Father in heaven. Hilary. On Matthew 4.27"
“The law of gospel love: The Lord has shown that we cannot have the good work of perfect love if we love only those from whom in turn we know the return of mutual love will be paid in kind. For we know that love of this sort is common even to nonbelievers and sinners. Hence the Lord wishes us to overcome the common law of human love by the law of gospel love, so that we may show the affection of our love not only toward those who love us but even toward our enemies. Thus we may imitate the example of true piety and our Father’s goodness. Chromatius. Tractate on Matthew 21.2.1"