"Love," in the Divinity, is to be understood both Essentially and Personally; for as Word is the name of the Son, so is Love that of the Holy Ghost; according to the two Processions, of which one is by mode of Intellect, and the other by that of Will. For the latter, owing to the poverty of language, no proper names exist; but as from the understanding faculty there proceeds something, namely, an intellectual conception of the thing known by the mind which knows, which is called a word, so likewise from the fact of something being loved there is formed an impression of the thing loved in the affection of the lover, in virtue of which the loved is in the lover. But no words are found expressive of the relation between the will and this impression of the object loved which is admitted to exist in the lover, or conversely, except love or affection. These properly express the inclination of the lover to the loved, and in this sense the word love is used Essentially; but when we mean the inclination of that which proceeds by mode of love to its principle, and conversely, so that by Love is understood love proceeding, it denotes the Person of the Holy Ghost.
And Love being understood in the Divinity after this twofold manner, Essentially and Notionally, the Father and the Son love Themselves according to the first sense, i.e. by their Essence, not by the Holy Ghost. In the second sense, to love is nothing else than to produce love by spiration, or to breathe love; as to speak is to produce words, or to flower is to produce flowers. Thus as a tree is said to flower with flowers, so the Father is said to express Himself and creatures by His Word or Son; and the Father and the Son to love by the Holy Ghost, i.e. Love Proceeding, both Themselves and us.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni