1 John 5:6-9
6. This is he that came by water and blood, even Jesus Christ; not by water only, but by water and blood. And it is the Spirit that beareth witness, because the Spirit is truth.
6. Hic est qui venit per aquam et sanguinem, Jesum Christum; non in aqua solum, sed in aqua et sanguine; et Spiritus est qui testificatur, quandoquidem Spiritus est veritas.
7. For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.
7. Nam tres sunt qui testificantur in coelo, Pater, Sermo, et Spiritus Sanctus; et hi tres unum sunt.
8. And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.
8. Et tres sunt qui testificantur in terra, Spiritus, aqua et sanguis; et hi tres in unum conveniunt.
9. If we receive the witness of men, the witness of God is greater: for this is the witness of God which he hath testified of his Son.
9. Si testimonium hominum recipimus, testimonium Dei majus est; quoniam hoc est testimonium Dei, quod testificatus est de Filio suo.
6 This is he that came That our faith may rest safely on Christ, he says the real substance of the shadows of the law appears in him. For I doubt not but that he alludes by the words water and blood to the ancient rites of the law. The comparison, moreover, is intended for this end, not only that we may know that the Law of Moses was abolished by the coming of Christ, but that we may seek in him the fulfillment of those things which the ceremonies formerly typified. And though they were of various kinds, yet under these two the Apostle denotes the whole perfection of holiness and righteousness, for by water was all filth washed away, so that men might come before God pure and clean, and by blood was expiation made, and a pledge given of a full reconciliation with God; but the law only adumbrated by external symbols what was to be really and fully performed by the Messiah.
John then fitly proves that Jesus is the Christ of the Lord formerly promised, because he brought with him that by which he sanctifies us wholly.
And, indeed, as to the blood by which Christ reconciled God, there is no doubt, but how he came by water may be questioned. But that the reference is to baptism is not probable. I certainly think that John sets forth here the fruit and effect of what he recorded in the Gospel history; for what he says there, that water and blood flowed from the side of Christ, is no doubt to be deemed a miracle. I know that such a thing does happen naturally to the dead; but it happened through God's purpose, that Christ's side became the fountain of blood and water, in order that the faithful may know that cleansing (of which the ancient baptisms were types) is found in him, and that they might know that what all the sprinklings of blood formerly presignified was fulfilled. On this subject we dwelt more at large on the ninth and tenth chapters of the Epistle to the Hebrews.
And it is the Spirit that beareth witness He shews in this clause how the faithful know and feel the power of Christ, even because the Spirit renders them certain; and that their faith might not vacillate, he adds, that a full and real firmness or stability is produced by the testimony of the Spirit. And he calls the Spirit truth, because his authority is indubitable, and ought to be abundantly sufficient for us.
7. There are three than bear record in heaven The whole of this verse has been by some omitted. Jerome thinks that this has happened through design rather than through mistake, and that indeed only on the part of the Latins. But as even the Greek copies do not agree, I dare not assert any thing on the subject. Since, however, the passage flows better when this clause is added, and as I see that it is found in the best and most approved copies, I am inclined to receive it as the true reading.  And the meaning would be, that God, in order to confirm most abundantly our faith in Christ, testifies in three ways that we ought to acquiesce in him. For as our faith acknowledges three persons in the one divine essence, so it is called in so really ways to Christ that it may rest on him.
When he says, These three are one, he refers not to essence, but on the contrary to consent; as though he had said that the Father and his eternal Word and Spirit harmoniously testify the same thing respecting Christ. Hence some copies have eis hen, "for one." But though you read hen eisin, as in other copies, yet there is no doubt but that the Father, the Word and the Spirit are said to be one, in the same sense in which afterwards the blood and the water and the Spirit are said to agree in one.
But as the Spirit, who is one witness, is mentioned twice, it seems to be an unnecessary repetition. To this I reply, that since he testifies of Christ in various ways, a twofold testimony is fitly ascribed to him. For the Father, together with his eternal Wisdom and Spirit, declares Jesus to be the Christ as it were authoritatively, then, in this ease, the sole majesty of the deity is to be considered by us. But as the Spirit, dwelling in our hearts, is an earnest, a pledge, and a seal, to confirm that decree, so he thus again speaks on earth by his grace.
But inasmuch as all do not receive this reading, I will therefore so expound what follows, as though the Apostle referred to the witnesses only on the earth.
8 There are three He applies what had been said of water and blood to it's own purpose, in order that they who reject Christ might have no excuse; for by testimonies abundantly strong and clear, he proves that it is he who had been formerly promised, inasmuch as water and blood, being the pledges and the effects of salvation, really testify that he had been sent by God. He adds a third witness, the Holy Spirit, who yet holds the first place, for without him the wafer and blood would have flowed without any benefit; for it is he who seals on our hearts the testimony of the water and blood; it is he who by his power makes the fruit of Christ's death to come to us; yea, he makes the blood shed for our redemption to penetrate into our hearts, or, to say all in one word, he makes Christ with all his blessings to become ours. So Paul, in Romans 1:4, after having said that Christ by his resurrection manifested himself to be the Son of God, immediately adds, "Through the sanctification of the Spirit." For whatever signs of divine glory may shine forth in Christ, they would yet be obscure to us and escape our vision, were not the Holy Spirit to open for us the eyes of faith.
Readers may now understand why John adduced the Spirit as a witness together with the water and the blood, even because it is the peculiar office of the Spirit, to cleanse our consciences by the blood of Christ, to cause the cleansing effected by it to be efficacious. On this subject some remarks are made at the beginning of the Second Epistle of Peter,  where he uses nearly the same mode of speaking, that is, that the Holy Spirit cleanses our hearts by the sprinkling of the blood of Christ. 
But from these words we may learn, that faith does not lay hold on a bare or an empty Christ, but that his power is at the same time vivifying. For to what purpose has Christ been sent on the earth, except to reconcile God by the sacrifice of his death? except the office of washing had been allotted to him by the Father?
It may however be objected, that the distinction here mentioned is superfluous, because Christ cleansed us by expiating our sins; then the Apostle mentions the same thing twice. I indeed allow that cleansing is included in expiation; therefore I made no difference between the water and the blood, as though they were distinct; but if any one of us considers his own infirmity, he will readily acknowledge that it is not in vain or without reason that blood is distinguished from the water. Besides, the Apostle, as it has been stated, alludes to the rites of the law; and God, on account of human infirmity, had formerly appointed, not only sacrifices, but also washings. And the Apostle meant distinctly to show that the reality of both has been exhibited in Christ, and on this account he had said before, "Not by water only," for he means, that not only some part of our salvation is found in Christ, but the whole of it, so that nothing is to be sought elsewhere.
9 If we receive the witness, or testimony, of men He proves, reasoning from the less to the greater, how ungrateful men are when they reject Christ, who has been approved, as he has related, by God; for if in worldly affairs we stand to the words of men, who may lie and deceive, how unreasonable it is that God should have less credit given to him, when sitting as it were on his own throne, where he is the supreme judge. Then our own corruption alone prevents us to receive Christ,, since he gives us full proof for believing in his power. Besides, he calls not only that the testimony of God which the Spirit imprints on our hearts, but also that which we derive from the water and the blood. For that power of cleansing and expiating was not earthly, but heavenly. Hence the blood of Christ is not to be estimated according to the common manner of men; but we must rather look to the design of God, who ordained it for blotting out sins, and also to that divine efficacy which flows from it.
 Calvin probably refers to printed copies in his day, and not to Greek MSS. As far as the authority of MSS. and versions and quotations goes, the passage is spurious, for it is not found in any of the Greek MSS prior to the 16th century, nor in any of the early versions, except the Latin, nor in some of the copies of that version; nor is it quoted by any of the early Greek fathers, nor by early Latin fathers, except a very few, and even their quotations have been disputed. These are facts which no refined conjectures can upset; and it is to be regretted that learned men, such as the late Bishop Burgess, should have labored and toiled in an attempt so hopeless as to establish the genuineness of this verse, or rather of a part of this verse, and of the beginning of the following. The whole passage is as follows, the spurious part being put within crotchets, -- 7. "For there are three who bear witness [in heaven, the Father, the Word, and the Holy Ghost; and these three are one: 8. And there are three who bear witness in earth,] the Spirit and the water and the blood; and these three agree in one." As to the construction of the passage, as far as grammar and sense are concerned, it may do with or without the interpolation equally the same. What has been said to the contrary on this point, seems to be nothing of a decisive character, in no way sufficient to shew that the words are not spurious. Indeed, the passage reads better without the interpolated words; and as to the sense, that is, the sense in which they are commonly taken by the advocates of their genuineness, it has no connection whatever with the general drift of the passage. -- Ed.  Although the commentary in 2Peter1:9 seems to be close to what Calvin is talking of here, it may be that perhaps the First Epistle of Peter might be the one he had in mind. - fj.  If we exclude the words deemed interpolated, we may read the passage thus: "This is he who came with water and blood, even Jesus Christ; not with water only, but with water and blood: the Spirit also beareth witness, for (or seeing that) the Spirit is truth (or, is true); because there are three who bear witness, the Spirit, the water, and the blood, and these three agree in one. We see hence a reason why the Spirit is said to be true, even because he is not alone, for the water and the blood concur with him. Thus a testimony is formed consistently with the requirement of the law. We hence also see the import of what is stated when the testimony of men is mentioned, as though he had said, The testimony of three men is received as valid, how much more valid is the testimony of God, which has three witnesses in its behalf? It is called God's testimony, because the witnesses have been ordered and appointed by him. When it is said that he came with water and blood, the meaning is, that he came, having water and blood; the proposition dia has sometimes this meaning, and it is changed in the second clause into en. We meet with similar instances in 2 Corinthians 3:11, and in 2 Corinthians 4:11. See Romans 2:27; 4:11 According to this construction, the explanation of Calvin is alone the right one, that the water means cleansing, and the blood expiation, the terms being borrowed from the rites of the law; and a reference is also made to the law when the witness of men is mentioned. -- Ed.
 Although the commentary in 2Peter1:9 seems to be close to what Calvin is talking of here, it may be that perhaps the First Epistle of Peter might be the one he had in mind. - fj.
 If we exclude the words deemed interpolated, we may read the passage thus: "This is he who came with water and blood, even Jesus Christ; not with water only, but with water and blood: the Spirit also beareth witness, for (or seeing that) the Spirit is truth (or, is true); because there are three who bear witness, the Spirit, the water, and the blood, and these three agree in one. We see hence a reason why the Spirit is said to be true, even because he is not alone, for the water and the blood concur with him. Thus a testimony is formed consistently with the requirement of the law. We hence also see the import of what is stated when the testimony of men is mentioned, as though he had said, The testimony of three men is received as valid, how much more valid is the testimony of God, which has three witnesses in its behalf? It is called God's testimony, because the witnesses have been ordered and appointed by him. When it is said that he came with water and blood, the meaning is, that he came, having water and blood; the proposition dia has sometimes this meaning, and it is changed in the second clause into en. We meet with similar instances in 2 Corinthians 3:11, and in 2 Corinthians 4:11. See Romans 2:27; 4:11 According to this construction, the explanation of Calvin is alone the right one, that the water means cleansing, and the blood expiation, the terms being borrowed from the rites of the law; and a reference is also made to the law when the witness of men is mentioned. -- Ed.