From the Forty-Fourth Festal Letter, for Easter 372

So when the servants of the chief priests and the scribes saw these things, and heard Jesus say, “Whoever is thirsty, let him come to me and drink,” they realized that this was not a mere man like themselves. They saw that this was the one who gave water to the saints, and the one the prophet Isaiah had announced. For he was truly the radiance of the light, and the Word of God. And so, like a river flowing from the fountain, he gave drink of old to Paradise as well; but now he gives the same gift of the Spirit to all people, and says, “If anyone is thirsty, let him come to me and drink. Whoever believes in me, as the Scripture says, rivers of living water will flow out of his belly.” This was not for a man to say, but for the living God, who truly grants life and gives the Holy Spirit. [a]