That water does not cleanse without the Spirit is shown by the witness of John and by the very form of the administration of the sacrament. And this is also declared to be signified by the pool in the Gospel and the man who was there healed. In the same passage, too, is shown that the Holy Spirit truly descended on Christ at His baptism, and the meaning of this mystery is explained.
19. The reason why you were told before not to believe only what you saw was that you might not say perchance, This is that great mystery |which eye hath not seen, nor ear heard, neither has it entered into the heart of man.| I see water, which I have been used to see every day. Is that water to cleanse me now in which I have so often bathed without ever being cleansed? By this you may recognize that water does not cleanse without the Spirit.
20. Therefore read that the three witnesses in baptism, the water, the blood, and the Spirit, are one, for if you take away one of these, the Sacrament of Baptism does not exist. For what is water without the cross of Christ? A common element, without any sacramental effect. Nor, again, is there the Sacrament of Regeneration without water: |For except a man be born again of water and of the Spirit, he cannot enter into the kingdom of God.| Now, even the catechumen believes in the cross of the Lord Jesus, wherewith he too is signed; but unless he be baptized in the Name of the Father, and of the Son, and of the Holy Spirit, he cannot receive remission of sins nor gain the gift of spiritual grace.
21. So that Syrian dipped himself seven times under the law, but you were baptized in the Name of the Trinity, you confessed the Father. Call to mind what you did: you confessed the Son, you confessed the Holy Spirit. Mark well the order of things in this faith: you died to the world, and rose again to God. And as though buried to the world in that element, being dead to sin, you rose again to eternal life. Believe, therefore, that these waters are not void of power.
22. Therefore it is said: |An angel of the Lord went down according to the season into the pool, and the water was troubled; and he who first after the troubling of the water went down into the pool was healed of whatsoever disease he was holden.| This pool was at Jerusalem, in which one was healed every year, but no one was healed before the angel had descended. Because of those who believed not the water was troubled as a sign that the angel had descended. They had a sign, you have faith; for them an angel descended, for you the Holy Spirit; for them the creature was troubled, for you Christ Himself, the Lord of the creature, works.
23. Then one was healed, now all are made whole; or more exactly, the Christian people alone, for in some even the water is deceitful. The baptism of unbelievers heals not but pollutes. The Jew washes pots and cups, as though things without sense were capable of guilt or grace. But do you wash this living cup of yours, that in it your good works may shine and the glory of your grace be bright. For that pool was as a type, that you might believe that the power of God descends upon this font.
24. Lastly, that paralytic was waiting for a man. And what man save the Lord Jesus, born of the Virgin, at Whose coming no longer the shadow should heal men one by one, but the truth should heal the whole. He it is, then, Whose coming down was being waited for, of Whom the Father said to John the Baptist: |Upon Whom thou shalt see the Spirit descending and abiding upon Him, this is He Who baptizeth with the Holy Spirit.| And John bare witness of Him, and said: |I saw the Spirit descending from heaven like a dove and abiding upon Him.| And why did the Spirit descend like a dove, but in order that you might see, that you might acknowledge, that that dove also which just Noah sent forth from the ark was a likeness of this dove, that you might recognize the type of the sacrament?
25. Perhaps you may object: Since that was a real dove which was sent forth, and the Spirit descended like a dove, how is it that we say that the likeness was there and the reality here, whereas in the Greek it is written that the Spirit descended in the likeness of a dove? But what is so real as the Godhead which abides for ever? Now the creature cannot be the reality, but only a likeness, which is easily destroyed and changed. So, again, because the simplicity of those who are baptized ought to be not in appearance but in reality, and the Lord says: |Be ye wise as serpents and simple as doves.| Rightly, then, did He descend like a dove, in order to admonish us that we ought to have the simplicity of the dove. And further we read of the likeness being put for the reality, both as regards Christ: |And was found in likeness as a man;| and as regards God the Father: |Nor have ye seen His likeness.|