Augustine of Hippo — as excerpted in the Catena Aurea on John 15:17-21

“(Tract. lxxxvii. 2) He saith this to the whole Church, which is often called the world; as, God was in Christ, reconciling the world unto Himself. (2 Cor. 5:19) The whole world then is the Church, and the whole world hateth the Church. The world hateth the world, the world in enmity, the world reconciled, the defiled world, the changed world. (Tract. lxxxviii. 4.). Here it may be asked, If the wicked can be said to persecute the wicked; e. g. if impious kings, and judges, who persecute the righteous, punish murderers and adulterers also; how are we to understand our Lord’s words, If ye were of the world, the world would love his own? In this way; The world is in them who punish these offences, and the world is in them who love them. The world then hates its own so far as it punishes the wicked, loves its own so far as it favours them. (Tract. lxxxvii. 4.). Again, if it be asked how the world loves itself, when it hates the means of its redemption, the answer is, that it loves itself with a false, not a true love, loves what hurts it; hates nature, loves vice. Wherefore we are forbidden to love what it loves in itself; commanded to love what it hates in itself. The vice in it we are forbidden, the nature in it we are commanded, to love. And to separate us from this lost world, we are chosen out of it, not by merit of our own, for we had no merits to begin with, not by nature which was radically corrupt, but by grace: But because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you.”