The basis of love 

6 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 which testifieth, that Christ is the truth. 7 And there are three who give testimony in heaven, the Father, the Word, and the Holy Ghost. And these three are one. 8 And there are three that give testimony on earth: the spirit, and the water, and the blood: and these three are one. 9 If we receive the testimony of men, the testimony of God is greater. For this is the testimony of God, which is greater, because he hath testified of his Son. 10 He that believeth in the Son of God, hath the testimony of God in himself. He that believeth not the Son, maketh him a liar: because he believeth not in the testimony which God hath testified of his Son.

 

 

God gives us eternal life through His Son 

11 And this is the testimony, that God hath given to us eternal life. And this life is in his Son. 12 He that hath the Son, hath life. He that hath not the Son, hath not life. 13 These things I write to you, that you may know that you have eternal life, you who believe in the name of the Son of God.

 

 

14 And this is the confidence which we have towards him: That, whatsoever we shall ask according to his will, he heareth us. 15 And we know that he heareth us whatsoever we ask: we know that we have the petitions which we request of him.

 

 

16 He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that any man ask. 17 All iniquity is sin. And there is a sin unto death.

 

 

18 We know that whosoever is born of God, sinneth not: but the generation of God preserveth him, and the wicked one toucheth him not. 19 We know that we are of God, and the whole world is seated in wickedness. 20 And we know that the Son of God is come: and he hath given us understanding that we may know the true God, and may be in his true Son. This is the true God and life eternal.

 

 

 

 

5:6 "by water and blood," to redeem the world, and spiritually regenerate mankind "by water" of baptism "and blood" of his passion, of which the baptism in water, and purifications by the shedding of blood, among the Jews, were so many significant types and figures. "Not by water only," in which allusion is evidently made to the Baptist, of whom it is everywhere pointedly asserted by the Evangelist—and the same is repeatedly asserted by himself—that he came to baptize in water only, and that he was sent by God for this purpose, and his baptism did not of itself remit sin, as it most probably, was a mere preparation for penance, and for the true baptism instituted by Christ. "But by water and blood." He came "by water," because he instituted baptism of water, whereof that which issued from his side while hanging on the cross was a sign; and "by blood," poured forth on the cross, from which baptism, and all the other channels of divine grace, derive their efficicacy. "And it is the Spirit that testifies, that Christ is the truth"; to the testimony of the water and blood, the Apostle adds that of the Holy Ghost, who testified to the Divinity of Christ, during his sacred life, working wonders in proof thereof; and after his death and resurrection, when descending on the Apostles, in the form of fiery tongues, he filled them with his graces, he also bore testimony to the same, in the many gifts which he bestowed on the faithful. (Bishop John McEvilly)

 

5:7-8 in heaven, the Father, the Word, and the Holy Spirit. And these three are one. And there are three that give testimony on earth: St. Jerome (Pref. in Epist. Canon.) observes that this verse had been erased by unbelievers, that is, the Arians, from some Greek copies. Therefore it is not found in the Syriac, Clement of Alexandria, Bede, Oecumenius, and some others. It is, however, the constant reading of the Latin Bibles, and the more correct Greek manuscripts and of many of the ancients, St. Athanasius, St. Augustine, St. Jerome, St. Cyprian, the Lateran Council, at which Greeks were present. Therefore it is certain that these words are to be taken as canonical Scripture. (Cornelius a Lapide)  In the Western Church it has been quoted as Divine Scripture from the earliest period. In the 3rd century, we have Tertullian (adv. Praxeam 25). St. Cyprian in the 3rd century did (Jubaianum, Ep, 73)... We are assured by St. Fulgentius, in the beginning of the 6th century, that, in these words, St. Cyprian referred to the 7th verse of 5th chapter of St. John. St. Jerome in the 5th century in his prologue to the Canonical Epistles, refers to the genuineness of this verse, and to the clear proof of the Trinity which it contains. St. Augustine quoted more than once as Divine Scripture, and a proof of the Trinity founded on them. Vigilius of Thapsus in the end of 5th century quotes the words… It is quoted in the prologue to the Canonical Epistles attributed to St. Jerome… It was commented on by ancient Interpreters, without hesitation. St Bernard, St. Bonaventure, St. Thomas… The clear and uniform testimony of the African Fathers and writers from the earliest date in favor of the genuineness of verse 7 is of the utmost importance, as it proves that these words were found in the early African Latin Version of the Vulgate, in existence before the days of Tertullian, who quotes from it. Now, this early African Latin Version represents a Greek manuscript, from which the version was made, of an earlier date than any Greek manuscript of the Scripture now extant. (Bishop John McEvilly) three are one: This number refers to the Trinity. (St. Eucharius of Lyons Formulas 10)  The spirit, and the water, and the blood: As the Father, the Word, and the Holy Spirit, all bear witness to Christ's divinity; so the spirit, which he yielded up, crying out with a loud voice upon the cross; and the water and blood that issued from his side, bear witness to his humanity, and are one; that is, all agree in one testimony. (Bishop Richard Challoner) The spirit:  St. Augustine, Nicholas of Lyra and the Glossa Ordinaria understand by the Spirit in this place the Holy Spirit shed forth at Pentecost. For He testified that Christ was God. Oecumenius understands by Spirit the Holy Spirit given at Baptism. (Cornelius a Lapide)

 

5:10 makes him a liar: That is, proclaims by this unbelief that God is a liar, having borne testimony to what is false, and rejects it as false, as if God were a liar. (Bishop John McEvilly)

 

 

5:14-15 This means that you must come to pray in the state in which He wanted you to come, that is, free from all hatred of a brother- for the person who does not pardon a neighbor for a trespass obtains nothing from God- and that you must ask for those things which are conductive to heavenly life and contribute to the glory of Christ. It is often the case that we do not know what should be asked from God, and, if the Spirit of Christ does not suggest to us what it is expedient to ask, we often ask for harmful things instead of salutary ones. But whenever we ask in the Spirit of Christ, we are sure that God hears our wishes and are likewise sure that He will grant us whatever we ask; and he can fulfill whatever he promises and he wants whatever contributes to our salvation. (Erasmus) 

 

5:16 The great difficulty in this passage is, to determine what is meant by "a sin unto death," and by "a sin not unto death." In the first place, it is clear the difference between them cannot consist in this, that one is venial, and the other mortal; for, St. John supposes the sin "not unto death," to take away spiritual life, "life shall be given to him who sins not unto death;" and hence, to be a mortal sin. The "sin," therefore, "which is unto death," must be a mortal sin, of some peculiar enormity or aggravation. Some interpreters understand it of willful apostasy from the faith; others of any mortal sin, wherein a person obstinately intends to persevere, and owing to which he refuses to do anything towards extricating himself from the wretched state in which he is; so that it refers to a sort of temporary impenitence in sin. Some understand it of final impenitence; but, this opinion is improbable; for, final impenitence is known only at death; but with reference to the sin, of which there is question here, St. John supposes, that we can know that our brother has fallen into it. The Greek is more expressive, if any one see his brother sinning, etc. Moreover, St. John would not have a person free to pray for one who died in final impenitence; whereas, here, he neither commands nor prohibits it, " I say not that any man ask." "There is a sin unto death." He uses these words to show that it is not without reason he made mention in the preceding, of a man sinning not unto death. "For that I say not that any man ask." The Apostle does not command us to pray for such a sinner, with the firm confidence of being heard in his behalf, with which we ordinarily present our petitions to God. The conversion of such a person is the result of a very great grace on the part of God, and requires an abundant degree of favor and acceptability with Him, on which every person cannot, without a certain degree of presumption, calculate. The Apostle does not prevent our praying for such a person; for, we ought to pray for our enemies and persecutors, be they ever so obstinate in evil; he only abstains from holding out certain hopes, that our prayers will be always heard, in the case of a sinner of this sort. Of course, whatever interpretation we adopt of this passage, we know from faith, that God wishes not the death of any sinner, but " that he be converted and live " (Ezech. 33: 1 1; Is. 3:18). There is no sin, for the remission of which, the Lord has not left power with his Church. "A sin unto death," probably refers to the sin of apostasy from the faith, and some other heinous sins, which are seldom, and with difficulty, remitted. The Apostle gives very little encouragement to such as pray for sinners like these, to expect that their petitions will be heard. (Bishop John McEvilly) I say not that any man ask: We ought to pray even for sinners, that they may be converted, and for the just that they may persevere and advance in holiness. Yet those who pray are heard not for all sinners but for some: since they are heard for the predestined, but not for those who are foreknown to death; even as the correction whereby we correct the brethren, has an effect in the predestined but not in the reprobate, according to Eccles. 7:14, "No man can correct whom God has despised." Hence it is written: "He that knows his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sins not to death." Now just as the benefit of correction must not be refused to any man so long as he lives here below, because we cannot distinguish the predestined from the reprobate, as Augustine says (De Correp. et Grat. 15), so too no man should be denied the help of prayer. (St. Thomas Aquinas Summa Theologica 2.83.7.r3)