Augustine of Hippo : What was it that flowed from Jesus' side if not the sacrament which believers receive? The Spirit, the blood and the water—the Spirit which he gave up, the blood and water which flowed from his side. The church is signified as being born from this blood and water. — SERMONS 5.3 Augustine of Hippo : I would not have thee mistake that place in the epistle of John the apostle where he saith, "There are three witnesses: the Spirit, and the water, and the blood: and the three are one." Lest haply thou say that the Spirit and the water and the blood are diverse substances, and yet it is said, "the three are one:" for this cause I have admonished thee, that thou mistake not the matter. For these are mystical expressions, in which the point always to be considered is, not what the actual things are, but what they denote as signs: since they are signs of things, and what they are in their essence is one thing, what they are in their signification another. If then we understand the things signified, we do find these things to be of one substance. Thus, if we should say, the rock and the water are one, meaning by the Rock, Christ; by the water, the Holy Ghost: who doubts that rock and water are two different substances? yet because Christ and the Holy Spirit are of one and the same nature, therefore when one says, the rock and the water are one, this can be rightly taken in this behalf, that these two things of which the nature is diverse, are signs of other things of which the nature is one. — Ten Homilies on 1 John 10 Augustine of Hippo : Three things then we know to have issued from the Body of the Lord when He hung upon the tree: first, the spirit: of which it is written, "And He bowed the head and gave up the spirit:" then, as His side was pierced by the spear, "blood and water." Which three things if we look at as they are in themselves, they are in substance several and distinct, and therefore they are not one. But if we will inquire into the things signified by these, there not unreasonably comes into our thoughts the Trinity itself, which is the One, Only, True, Supreme God, Father and Son and Holy Ghost, of whom it could most truly be said, "There are Three Witnesses, and the Three are One:" so that by the term Spirit we should understand God the Father to be signified; as indeed it was concerning the worshipping of Him that the Lord was speaking, when He said, "God is a Spirit:" by the term, blood, the Son; because "the Word was made flesh:" and by the term water, the Holy Ghost; as, when Jesus spake of the water which He would give to them that thirst, the evangelist saith, "But this said He of the Spirit which they that believed on Him were to receive." — Ten Homilies on 1 John 10 Augustine of Hippo : Moreover, that the Father, Son, and Holy Ghost are "Witnesses," who that believes the Gospel can doubt, when the Son saith, "I am one that bear witness of myself, and the Father that sent me, He beareth witness of me." Where, though the Holy Ghost is not mentioned, yet He is not to be thought separated from them. Howbeit neither concerning the Spirit hath He kept silence elsewhere, and that He too is a witness hath been sufficiently and openly shown. For in promising Him He said, "He shall bear witness of me." These are the "Three Witnesses, and the Three are One, because of one substance. But whereas, the signs by which they were signified came forth from the Body of the Lord, herein they figured the Church preaching the Trinity, that it hath one and the same nature: since these Three in threefold manner signified are One, and the Church that preacheth them is the Body of Christ. — Ten Homilies on 1 John 10 Ishodad of Merv : The three things are one because everything was accomplished by the one Christ. — COMMENTARIES Leo the Great : "This is He that came by water and blood, Jesus Christ: not by water only, but by water and blood. And it is the Spirit that testifieth, because the Spirit is the truth, because there are three that bear witness, the Spirit, the water and the blood, and the three are one." The Spirit, that is, of sanctification, and the blood of redemption, and the water of baptism: because the three are one, and remain undivided, and none of them is separated from this connection; because the catholic Church lives and progresses by this faith, so that in Christ Jesus neither the manhood without the true Godhead nor the Godhead without the true manhood is believed in. — LETTERS 28 Oecumenius : For there are three that bear witness: the Spirit, the water, and the blood; and these three are one. Therefore, since three bear witness to Jesus' adoption, namely baptism, crucifixion, and resurrection, there is no uncertainty in the Lord's adoption: by which adoption He also granted us, as He who was the first fruits of the entire human mass (Rom. 11:16), to be children of God. And these three are united in one Christ: for this is what it signifies, saying: "These three are one," that is, as a testimony concerning Christ. It should be noted that some of the fathers received the Spirit, not because of the resurrection, but the Father Himself when He cried out in the Jordan: "This is my beloved Son (Matt. 17:5);" because God is also called Spirit, as we have predicted. — Commentary on 1 John