6 In what sense then was it said a while ago, “Love is of God;” and now, “Love IS God?” For God is Father and Son and Holy Ghost: the Son, God of God, the Holy Ghost, God of God; and these three, one God, not three Gods. If the Son be God, and the Holy Ghost God, and that person loves in whom dwells the Holy Ghost: therefore “Love is God;” but “IS God,” because “Of God.” For you have both in the epistle; both, “Love is of God,” and, “Love is God.” Of the Father alone the Scripture has it not to say, that He is “of God:” but when you hear that expression, “Of God,” either the Son is meant, or the Holy Ghost. Because while the apostle says, “The love of God is shed abroad in our hearts by the Holy Spirit which is given unto us:” let us understand that He who subsists in love is the Holy Ghost. For it is even this Holy Spirit, whom the bad cannot receive, even He is that Fountain of which the Scripture says, “Let the fountain of your water be your own, and let no stranger partake with you.” For all who love not God, are strangers, are antichrists. And though they come to the churches, they cannot be numbered among the children of God; not to them belongs that Fountain of life. To have baptism is possible even for a bad man; to have prophecy is possible even for a bad man. We find that king Saul had prophecy: he was persecuting holy David, yet was he filled with the spirit of prophecy, and began to prophesy. To receive the sacrament of the body and blood of the Lord is possible even for a bad man: for of such it is said, “He that eats and drinks unworthily, eats and drinks judgment to himself.” To have the name of Christ is possible even for a bad man; i.e. even a bad man can be called a Christian: as they of whom it is said, “They polluted the name of their God.” I say, to have all these sacraments is possible even for a bad man; but to have charity, and to be a bad man, is not possible. This then is the peculiar gift, this the “Fountain” that is singly one's “own.” To drink of this the Spirit of God exhorts you, to drink of Himself the Spirit of God exhorts you.
7. “In this was manifested the love of God in us.” Behold, in order that we may love God, we have exhortation. Could we love Him, unless He first loved us? If we were slow to love, let us not be slow to love in return. He first loved us; not even so do we love. He loved the unrighteous, but He did away the unrighteousness: He loved the unrighteous, but not unto unrighteousness did He gather them together: He loved the sick, but He visited them to make them whole. “Love,” then, “is God.” “In this was manifested the love of God in us, because that God sent His only-begotten Son into the world, that we may live through Him.” As the Lord Himself says: “Greater love than this can no man have, that a man lay down his life for his friends:” and there was proved the love of Christ towards us, in that He died for us: how is the love of the Father towards us proved? In that He “sent His only Son” to die for us: so also the apostle Paul says: “He that spared not His own Son, but delivered Him up for us all, how has He not with Him also freely given us all things?” Behold the Father delivered up Christ; Judas delivered Him up; does it not seem as if the thing done were of the same sort? Judas is “traditor,” one that delivered up, [or, a traitor]: is God the Father that? God forbid! Do you say. I do not say it, but the apostle says, He that spared not His own Son, but “tradidit Eum” delivered Him up for us all. Both the Father delivered Him up, and He delivered up Himself. The same apostle says: “Who loved me, and delivered Himself up for me.” If the Father delivered up the Son; and the Son delivered up Himself, what has Judas done? There was a “traditio” (delivering up) by the Father; there was a “traditio” by the Son; there was a “traditio” by Judas: the thing done is the same, but what is it that distinguishes the Father delivering up the Son, the Son delivering up Himself, and Judas the disciple delivering up his Master? This: that the Father and the Son did it in love, but Judas did this in treacherous betrayal. You see that not what the man does is the thing to be considered; but with what mind and will he does it. We find God the Father in the same deed in which we find Judas; the Father we bless, Judas we detest. Why do we bless the Father, and detest Judas? We bless charity, detest iniquity. How great a good was conferred upon mankind by the delivering up of Christ! Had Judas this in his thoughts, that therefore he delivered Him up? God had in His thoughts our salvation by which we were redeemed; Judas had in his thoughts the price for which he sold the Lord. The Son Himself had in His thoughts the price He gave for us, Judas in his the price he received to sell Him. The diverse intention therefore makes the things done diverse. Though the thing be one, yet if we measure it by the diverse intentions, we find the one a thing to be loved, the other to be condemned; the one we find a thing to be glorified, the other to be detested. Such is the force of charity. See that it alone discriminates, it alone distinguishes the doings of men.
Source: Homilies on the First Epistle of John (New Advent)