Ambrose of Milan, on Isa 11:2

So, then, the Holy Spirit is the river, and the abundant river, which according to the Hebrews flowed from Jesus in the lands, as we have received it prophesied by the mouth of Isaiah. This is the great river that flows always and never fails. And not only a river, but also one of copious stream and overflowing greatness, as also David said: "The stream of the river makes glad the city of God."60For neither is that city, the heavenly Jerusalem, watered by the channel of any earthly river, but that Holy Spirit, proceeding from the fount of life, by a short draught of whom we are satiated, seems to flow more abundantly among those celestial thrones, dominions and powers, angels and archangels, rushing in the full course of the seven virtues of the Spirit. For if a river rising above its banks overflows, how much more does the Spirit, rising above every creature, when he touches the low-lying fields of our minds, as it were, make glad that heavenly nature of the creatures with the larger fertility of his sanctification.
And let it not trouble you that either here it is said "rivers" or elsewhere "seven Spirits," for by the sanctification of these seven gifts of the Spirit, as Isaiah said, is signified the fullness of all virtue; the Spirit of wisdom and understanding, the Spirit of counsel and strength, the Spirit of knowledge and godliness, and the Spirit of the fear of God. One, then is the river, but many the channels of the gifts of the Spirit. This river, then, goes forth from the fount of life.