Brad at Resident Theology drew my attention today to this quote from Augustine's On the Trinity:
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.
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?