Isaiah 48:18

Set before yourself any river. It springs from its fountain but is of one nature, of one brightness and beauty. And you assert rightly that the Holy Spirit is of one substance, brightness and glory with the Son of God and with God the Father. I will sum up everything in the oneness of the qualities without any dispute over degrees of greatness. For in this point also Scripture has provided for us. For the Son of God says, "Whoever shall drink of the water that I will give him, it shall become in him a well of water springing up unto everlasting life." This well is clearly the grace of the Spirit, a stream proceeding from the living Fountain. The Holy Spirit, then, is also the fountain of eternal life.You observe, then, from his words that the unity of the divine greatness is pointed out and that Christ cannot be denied to be a fountain even by heretics, since the Spirit, too, is called a fountain. The Spirit is called a river, too, just as the Father said, "Behold, I come down on you like a river of peace, and like a stream overflowing the glory of the Gentiles." And who can doubt that the Son of God is the river of life from whom the streams of eternal life flowed forth?

This water is good, then. I mean here the grace of the Spirit. Who will give this Fountain to my heart? Let it spring up in me, let that which gives eternal life flow on me. Let that Fountain overflow on us and not flow away. For Wisdom says, "Drink water out of your own vessels and from the fountains of your own wells, and let your waters flow abroad in your streets." How shall I keep this water so that it does not seep out or glide away? How shall I preserve my vessel, lest any crack of sin penetrating it should let the water of eternal life exude? Teach us, Lord Jesus, teach us as you taught your apostles, saying, "Lay not up for yourselves treasures on the earth, where rust and moth destroy and where thieves break through and steal."8Our rust is wantonness, our rust is lust, our rust is luxury, which dim the keen vision of the mind with the filth of vices. Again, our moth is Arius, our moth is Photinus, who rend the holy vesture of the church with their impiety, and desiring to separate the indivisible unity of the divine power, gnaw the precious veil of faith with sacrilegious tooth. The water is spillled if Arius has imprinted his tooth, it flows away if Photinus has planted his sting in anyone's vessel.… If you seek Jesus, forsake the broken cisterns, for Christ did not make it his custom to sit by a pool but by a well. There that Samaritan woman found him, she who believed, she who wished to draw water. Although you ought to have come in early morning, nevertheless if you come later, even at the sixth hour, you will find Jesus wearied with his journey. He is weary, but it is because of you, because he has long looked for you, your unbelief has long wearied him. Yet he is not offended if you only come now. He asks to drink who is about to give. But he drinks not the water of a stream flowing by, but your salvation. He drinks your good dispositions. He drinks the cup, that is, the passion that atoned for your sins, that you, drinking of his sacred blood, might quench the thirst of this world.