On One Single Hatred:

The Lawgiver of our life has enjoined upon us one single hatred. I mean, that of the Serpent: for no other purpose has He bidden us exercise this faculty of hatred, but as a resource against wickedness. "I will put enmity," He says, "between thee and him." Since wickedness is a complicated and multifarious thing, the Word allegorizes it by the Serpent, the dense array of whose scales is symbolic of this multiformity of evil. And we by working the will of our Adversary make an alliance with this serpent, and so turn this hatred against one another, and perhaps not against ourselves alone, but against Him Who gave the commandment; for He says, "Thou shalt love thy neighbour and hate thine enemy," commanding us to hold the foe to our humanity as our only enemy, and declaring that all who share that humanity are the neighbours of each one of us. But this gross-hearted age has disunited us from our neighbour, and has made us welcome the serpent, and revel in his spotted scales. I affirm, then, that it is a lawful thing to hate God's enemies, and that this kind of hatred is pleasing to our Lord: and by God's enemies I mean those who deny the glory of our Lord, be they Jews, or downright idolaters, or those who through Arius' teaching idolize the creature, and so adopt the error of the Jews. Now when the Father, the Son, and the Holy Spirit, are with orthodox devotion being glorified and adored by those who believe that in a distinct and unconfused Trinity there is One Substance, Glory, Kingship, Power, and Universal Rule, in such a case as this what good excuse for fighting can there be? At the time, certainly, when the heretical views prevailed, to try issues with the authorities, by whom the adversaries' cause was seen to be strengthened, was well; there was fear then lest our saving Doctrine should be over-ruled by human rulers. But now, when over the whole world from one end of heaven to the other the orthodox Faith is being preached, the man who fights with them who preach it, fights not with them, but with Him Who is thus preached.

St. Gregory of Nyssa, Excerpt from LETTER XVII. TO EUSTATHIA, AMBROSIA, AND BASILISSA(1)