"Nothing is more excellent than this gift of God. This alone is what distinguishes between the sons of the eternal kingdom and the sons of eternal perdition. Other endowments too are given through the Holy Spirit, but without charity they are of no use. Unless therefore the Holy Spirit is imparted to someone to make him a lover of God and neighbor, he cannot transfer from the left hand to the right. Why is the Spirit distinctively called gift? Only because of the love without which the man who has not got it, though he speak with the tongues of men and of angels, is booming bronze and a clashing cymbal; and if he has prophecy and knows all mysteries and all knowledge and has all faith so as to move mountains, it is nothing; and if he distributes all his substance, and if he gives over his body to burn, it does him no good. What a great good must it be then, without which such great goods cannot bring anyone to eternal life! But if a man has this love or charity (they are two names for one thing), and does not speak with tongues or have prophecy or know all mysteries and all knowledge or distribute all his property to the poor, either because he has not got any to distribute or because he is prevented by some family obligation, it brings him home to the kingdom; yes, even faith is only rendered of any use for this purpose by charity. Faith there can indeed be without charity, but it cannot be of any use. That is why even the apostle Paul says, "In Christ Jesus neither circumcision nor [uncircumcision] is of any value, but faith which works through love" (Gal 5:6); in this way he distinguishes it from the faith with which even the demons believe and tremble. So the love which is from God and is God is distinctively the Holy Spirit; through him the charity of God is poured out in our hearts, and through it the whole triad dwell in us. This is the reason why it is most apposite that the Holy Spirit, while being God, should also be called the gift of God. And this gift, surely, is distinctively to be understood as being the charity which brings us through to God, without which no other gift of God at all can bring us through to God."
--Augustine, De Trinitate XV.32 (translated by Edmund Hill, OP)