Of Loving Our Enemies
And that we should be kindly disposed, not only towards those of our own stock, as some suppose, Isaiah the prophet said: “Say to those that hate you, and that cast you out, You are our brethren, that the name of the Lord may be glorified, and be apparent in their joy.” And the Gospel says: “Love your enemies, and pray for them that despitefully use you. For if you love them who love you, what reward will you have? This do also the robbers and the publicans.” And those that do good it teaches not to boast, lest they become men-pleasers. For it says: “Let not your left hand know what your right hand does.” Moreover, concerning subjection to authorities and powers, and prayer for them, the divine word gives us instructions, in order that “we may lead a quiet and peaceable life.” And it teaches us to render all things to all, “honour to whom honour, fear to whom fear, tribute to whom tribute; to owe no man anything, but to love all.”
Source: Theophilus to Autolycus (New Advent)