Drink we of “living water, springing up into everlasting life”; “but this spoke” the Savior “of the Spirit, which they that believe in Him should receive”. For observe what He says, “He that believes in Me (not simply this, but), as the Scripture has said (thus He has sent you back to the Old Testament), out of his belly shall flow rivers of living water”, not rivers perceived by sense and merely watering the earth with its thorns and trees, but bringing souls to the light. And in another place, He says, “But the water that I shall give him, shall be in him a well of living water springing up into everlasting life”, — a new kind of water living and springing up, springing up unto them who are worthy.
And why did He call the grace of the Spirit water? Because by water all things subsist; because water brings forth grass and living things; because the water of the showers comes down from heaven; because it comes down one in form, but works in many forms. For one fountain waters the whole of Paradise, and one and the same rain comes down upon all the world, yet it becomes white in the lily, and red in the rose, and purple in violets and hyacinths, and different and varied in each several kind: so it is one in the palm-tree, and another in the vine, and all in all things; and yet is one in nature, not diverse from itself; for the rain does not change itself and come down first as one thing, then as another, but adapting itself to the constitution of each thing which receives it, it becomes to each what is suitable. Thus also the Holy Spirit, being one and of one nature and indivisible, divides to each His grace, “according as He will”: and as the dry tree, after partaking of water, puts forth shoots, so also the soul in sin, when it has been through repentance made worthy of the Holy Spirit, brings forth clusters of righteousness. And though He is One in nature, yet many are the virtues which by the will of God and in the Name of Christ He works. For He employs the tongue of one man for wisdom; the soul of another He enlightens by Prophecy; to another He gives power to drive away devils; to another He gives to interpret the divine Scriptures. He strengthens one man’s self-command; He teaches another the way to give alms; another He teaches to fast and discipline himself; another He teaches to despise the things of the body; another He trains for martyrdom: diverse in different men, yet not diverse from Himself, as it is written, “But the manifestation of the Spirit is given to every man to profit withal. For to one is given through the Spirit the word of wisdom; and to another the word of knowledge according to the same Spirit; to another faith, in the same Spirit; and to another gifts of healing, in the same Spirit; and to another workings of miracles; and to another prophecy; and to another discerning of spirits; and to another various kinds of tongues; and to another the interpretation of tongues: but all these works that one and the same Spirit, dividing to every man severally as He will.”
-from Catechetical Homily 16