8 All these things, my brethren,— “because we have known That which is from the beginning, because we are strong, because we have known the Father,”— do all these, while they in a manner commend knowledge, not commend charity? If we have known, let us love: for knowledge without charity saves not. “Knowledge puffs up, charity edifies.” If you have a mind to confess and not love, you begin to be like the demons. The demons confessed the Son of God, and said, “What have we to do with You?” and were repulsed.
Confess and embrace. For those feared for their iniquities; love ye Him that forgives your iniquities. But how can we love God, if we love the world? He prepares us therefore to be inhabited by charity. There are two loves: of the world, and of God: if the love of the world inhabit, there is no way for the love of God to enter in: let the love of the world make way, and the love of God inhabit; let the better have place. You loved the world: love not the world: when you have emptied your heart of earthly love, you shall drink in love Divine: and thenceforth begins charity to inhabit you, from which can nothing of evil proceed.
Hear therefore his words, how he goes to work in the manner of one that makes a clearance. He comes upon the hearts of men as a field that he would occupy: but in what state does he find it? If he finds a wood, he roots it up; if he finds the field cleared, he plants it. He would plant a tree there, charity. And what is the wood he would root up? Love of the world. Hear him, the rooter up of the wood! “Love not the world,” (for this comes next,) “neither the things that are in the world; if any man love the world, the love of the Father is not in him.”
Source: Homilies on the First Epistle of John (New Advent)