By St. Augustine
There is no gift of God more excellent than this. It alone distinguishes the sons of the eternal kingdom and the sons of eternal perdition. Other gifts, too, are given by the Holy Spirit; but without love they profit nothing. Unless, therefore, the Holy Spirit is so far imparted to each, as to make him one who loves God and his neighbor, he is not removed from the left hand to the right. Nor is the Spirit specially called the Gift, unless on account of love. And he who has not this love, “though he speak with the tongues of men and angels, is sounding brass and a tinkling cymbal; and though he have the gift of prophecy, and know all mysteries and all knowledge, and though he have all faith, so that he can remove mountains, he is nothing; and though he bestow all his goods to feed the poor, and though he give his body to be burned, it profiteth him nothing.”
How great a good, then, is that without which goods so great bring no one to eternal life! But love or charity itself,–for they are two names for one thing,–if he have it that does not speak with tongues, nor has the gift of prophecy, nor knows all mysteries and all knowledge, nor gives all his goods to the poor, either because he has none to give or because some necessity hinders, nor delivers his body to be burned, if no trial of such a suffering overtakes him, brings that man to the kingdom, so that faith itself is only rendered profitable by love, since faith without love can indeed exist, but cannot profit. And therefore also the Apostle Paul says, “In Christ Jesus neither circumcision availeth anything, nor uncircumcision, but faith that worketh by love:” so distinguishing it from that faith by which even “the devils believe and tremble.” Love, therefore, which is of God and is God, is specially the Holy Spirit, by whom the love of God is shed abroad in our hearts, by which love the whole Trinity dwells in us. And therefore most rightly is the Holy Spirit, although He is God, called also the gift of God. And by that gift what else can properly be understood except love, which brings to God, and without which any other gift of God whatsoever does not bring to God? . . .
Wherefore, if Holy Scripture proclaims that God is love, and that love is of God, and works this in us that we abide in God and He in us, and that hereby we know this, because He has given us of His Spirit, then the Spirit Himself is God, who is love. Next, if there be among the gifts of God none greater than love, and there is no greater gift of God than the Holy Spirit, what follows more naturally than that He is Himself love, who is called both God and of God? And if the love by which the Father loves the Son, and the Son loves the Father, ineffably demonstrates the communion of both, what is more suitable than that He should be specially called love, who is the Spirit common to both? For this is the sounder thing both to believe and to understand, that the Holy Spirit is not alone love in that Trinity, yet is not specially called love to no purpose.