That is the noblest revenge, and in those moments David had intimate knowledge of the spirit of his Lord. "If thine enemy hunger, feed him!"
Evil for good is devil-like. To receive a favour and to return a blow! To obtain the gift of language, and then to use one's speech to curse the giver! To use a sacred sword is unholy warfare! All this is devil-like.
Evil for evil is beast-like. Yes, the dog bites back when it is bitten. The dog returns snarl for snarl, venom for venom. And if, when I have been injured, I "pay a man back in his own coin," if I "give him as good as he gave," I am living on the plane of the beast.
Good for good is man-like. When I requite a man's kindness by kindness! When I send presents to one who loads me with benefits! This is a true and manly thing to do, and lifts us far above the beast.
Good for evil is God-like. Yes, that lifts me into "the heavenly places in Christ Jesus." Then I have "the mind of Christ." Then do I unto others as my Saviour has done unto me.