31 And just as you want men to do to you, you also do to them likewise. 32 But if you love those who love you, what credit is that to you? For even sinners love those who love them. 33 And if you do good to those who do good to you, what credit is that to you? For even sinners do the same. 34 And if you lend to those from whom you hope to receive back, what credit is that to you? For even sinners lend to sinners to receive as much back. 35 But love your enemies, do good, and lend, hoping for nothing in return; and your reward will be great, and you will be sons of the Most High. For He is kind to the unthankful and evil. 36 Therefore be merciful, just as your Father also is merciful.
St. John Chrysostom in his Homily XVIII on Matthew V said:
“What then can we deserve, who are commanded to emulate God, and are perhaps in a manner of life hardly even equal to publicans? For if ‘to love those who love us’ is the part of the publicans, sinners, and heathens: when we do not even do this (and we do not do it, as long as we envy our brothers who are in honor), what penalty will we not incur, commanded as we are to surpass the scribes, and taking our place below the heathens? How then will we behold the kingdom, pray tell? How will we set foot on that holy threshold, who do not surpass even the publicans? …Bearing in mind all the things that have been said, let us then show forth great love even towards our enemies; and let us cast away that ridiculous custom, to which many of the more thoughtless give way: waiting for those who meet them to address them first.”
Augustine the Blessed said in his Tractates on the Gospel of John:
“We are also prohibited both from loving that world and, if we understand rightly, are commanded to love it. We are prohibited, of course, where it is said to us, ‘Do not love the world.’ But we are commanded when it is said to us, ‘Love your enemies.’ They are the world, which hates us. Therefore we are both prohibited from loving in it what the world itself loves, and we are commanded to love in it what the world hates, namely, the handiwork of God and the various comforts of His goodness. We are prohibited from loving the fault in it and are commanded to love its nature. So we rightly love and hate it, although it perversely loves and hates itself.”