According to Richard of St. Victory (On the Trinity), God is the fullness and perfection of all goodness. Plotinus said as much.
But then Richard adds that nothing is better than charity, something that Plotinus does not say. For Richard, charity cannot be a solitary enterprise; charity must be directed at another: “no one is properly said to have charity on the basis of his own private love of himself.”
Thus, “it is necessary for love to be directed toward another for it to be charity.” In fact, it’s not enough for love to be directed at another. Perfect charity requires that the beloved be equal to the lover. Shared love among equals is the highest form of love. This means, first, that “If there is supreme love, then there is a plurality of persons” and then “if there is supreme love, then there is an equality of persons.”
This might seem to support only a binity, or even an infinite of persons. If love is fulfilled in love for others, then an infinite number of equal divine others seems best. Why three and only three?
Richard begins his answer by saying that “the greatest love cannot lack in anything.” To be perfect, then, a person must wish that another be loved just as he is loved, and also “wishes that another person be loved equally by the one whom he loves supremely and by whom he is supremely loved.”The fullness of love is what Richard calls condilectio, shared love, love shared by two persons for a third: “When one person gives love to another and he alone loves only the other, there certainly is love (dilectio) but it is not a shared love (condilectio). When two love each other mutually and give to each other the affection of supreme longing; when the affection of the first goes out to the second and the affection of the second goes out to the first and tends as it were in diverse ways – in this case there certainly is love (dilectio) on both sides, but it is not shared love (condilectio). Shared love (condilectio) is properly said to exist when a third person is loved by two persons harmoniously and in community, and the affection of the two persons is fused into one affection by the flame of love for a third. From these things it is evident that shared love (condilectio) would have no place in Divinity itself if a third person were lacking to the other two persons.”
It seems at times as if Richard is striving to fit the Trinity into a more encompassing framework of how-love-works. And it may not be altogether clear how Richard’s answer avoids the problem of a proliferation of divine Persons. Still, Richard’s is one of the great medieval developments of Augustine’s Trinitarian theology, and continues to inspire theologians today.