The Liturgy’s prayer for Saint Ambrose may be found here.
But lest perchance any one should speak against as it were
the littleness of the Spirit and from this should endeavour to establish a
difference in greatness, arguing that water seems to be but a small part of a
Fount, although examples taken from creatures seem by no means suitable for
application to the Godhead; yet lest they should judge anything injuriously
from this comparison taken from creatures, let them learn that not only is the Holy
Spirit called Water, but also a River, as we read: “From his belly shall flow
rivers of living water. But this He said of the Spirit, Whom they were
beginning to receive, who were about to believe in Him” (Jn 7:38-39).
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 (Is 66:12). This is the great River which 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.
For 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 as it were low-lying fields of our
minds, make glad that heavenly nature of the creatures with the larger
fertility of His sanctification. (St. Ambrose, On the Holy Spirit, Book One, 176-178)