Bede : Since there are three who bear witness on earth, etc. The Spirit has borne witness that Jesus is truth, when it descended upon Him at His baptism. For if he were not truly the Son of God, by no means would the Holy Spirit have come to Him with such a great manifestation. Water and blood also bore witness that Jesus is truth, when from His side on the cross, after He had died, they flowed out: which could not have happened at all, if He did not have a true nature of flesh. And also this that before His passion, when He prayed, His sweat became like great drops of blood falling to the ground (Luke 22), gives testimony to the truth of the flesh He had assumed. Nor should it be ignored that in this also blood and water bore witness to Him, that from His side after death they flowed out vividly, which was against the nature of dead bodies, and therefore was apt for mysteries, and was fitting as a testimony of the truth, namely showing that the very body of the Lord would live more gloriously after being resurrected, and that His very death would grant us life. This too, that His sweat fell to the ground like drops of blood, bore witness to that holy mystery that He would wash the whole Church all over the world with His blood. Therefore, there are three who bear witness to the truth. — Commentary on the Catholic Epistles Bede : And (he says) the three are one. For these remain indivisible, and none of them is separated from its connection, because divinity is not to be believed without true humanity, nor humanity without true divinity. But in us also these are one, not by nature of the same substance, but by the operation of the same mystery. For, as the blessed Ambrose says: "The Spirit renews the abiding, water leads to washing, blood pertains to redemption." For the Spirit has made us sons of God through adoption, the wave of the sacred font washes us, the blood of the Lord has redeemed us. Therefore, one invisible, the other visible testimony, follows the spiritual sacrament. — Commentary on the Catholic Epistles Cyprian : The Lord says, "I and the Father are one;" and again it is written of the Father, and of the Son, and of the Holy Spirit, "And these three are one." And does any one believe that this unity which thus comes from the divine strength and coheres in celestial sacraments, can be divided in the Church, and can be separated by the parting asunder of opposing wills? He who does not hold this unity does not hold God's law, does not hold the faith of the Father and the Son, does not hold life and salvation. — Treatise 1. On the Unity of the Church