1Jo 5:1
5:1 Whosoever {1} believeth that Jesus is the {a} Christ is born
    of God: and every one that loveth him that begat loveth {b}
    him also that is begotten of him.

 (1) He advances in the same argument, showing how both those
     loves come to us, from that love with which God loves us,
     that is, by Jesus our mediator laid hold on by faith, in
     whom we are made the children of God, and do love the
     Father from whom we are begotten, and also our brothers who
     are begotten with us.
    (a) Is the true Messiah.
    (b) By one, he means all the faithful.

1Jo 5:2
5:2 {2} By this we know that we love the children of God, when
    we love God, and keep his {c} commandments.

 (2) The love of our neighbour depends on the love with which we
     love God, that this last must go before the first: of which
     it follows, that that is not to be called love, when men
     agree together to do evil, neither that, when as in loving
     our neighbours, we do not respect God's commandments.
    (c) There is no love where there is no true doctrine.

1Jo 5:3
5:3 {3} For this is the love of God, that we keep his
    commandments: {4} and his commandments are not {d} grievous.

 (3) The reason: to love God, is to keep his commandments, which
     being so, and seeing that both the loves are commanded by
     the same lawmaker, (as he taught before) it follows also,
     that we do not love our neighbours, when we break God's
     commandments.
 (4) Because experience teaches us that there is no ability in
     our flesh, neither will to perform God's commandments,
     therefore lest the apostle should seem, by so often putting
     them in mind of the keeping of the commandments of God, to
     require things that are impossible, he pronounces that the
     commandments of God are not in any way grievous or
     burdensome, that we can be oppressed with the burden of
     them.
    (d) To those who are regenerate, that is to say, born again,
        who are led by the Spirit of God, and are through grace
        delivered from the curse of the law.

1Jo 5:4
5:4 {5} For whatsoever is born of God overcometh the world: {6}
    and this is the victory that {e} overcometh the world,
    [even] our {f} faith.

 (5) A reason: Because by regeneration we have received strength
     to overcome the world, that is to say, whatever strives
     against the commandments of God.
 (6) He declares what that strength is, that is, faith.
    (e) He uses the time that is past, to give us to understand,
        that although we are in the battle, yet undoubtedly we
        shall be conquerors, and are most certain of the
        victory.
    (f) Which is the instrumental cause, and as a means and hand
        by which we lay hold on him, who indeed performs this,
        that is, has and does overcome the world, even Christ
        Jesus.

1Jo 5:5
5:5 {7} Who is he that overcometh the world, but he that
    believeth that Jesus is the Son of God?

 (7) Moreover he declares two things, the one, what true faith
     is, that is, that which rests on Jesus Christ the Son of
     God alone: on which follows the other, that is, that this
     strength is not proper to faith, but by faith as an
     instrument is drawn from Jesus Christ the Son of God.

1Jo 5:6
5:6 {8} This is he that came by water and blood, [even] Jesus
    Christ; {9} not by water only, but by water and blood. And
    it is the {g} Spirit that beareth witness, because the
    Spirit is truth.

 (8) He proves the excellency of Christ, in whom only all things
     are given us by six witnesses, three heavenly, and three
     earthly, who wholly and completely agree together.  The
     heavenly witnesses are, the Father who sent the Son, the
     Word itself, which became flesh, and the Holy Spirit.  The
     earthly witnesses are water, (that is our sanctification)
     blood, (that is, our justification) the Spirit, (that is,
     acknowledging of God the Father in Christ by faith) through
     the testimony of the Holy Spirit.
 (9) He warns us not to separate water from blood (that is
     sanctification from justification, or righteousness, begun
     from righteousness imputed) for we do not stand on
     sanctification, but so far as it is a witness of Christ's
     righteousness imputed to us: and although this imputation
     of Christ's righteousness is never separated from
     sanctification, yet it is the only matter of our salvation.

    (g) Our spirit which is the third witness, testifies that
        the holy Sprit is truth, that is to say, that that is
        true which he tells us, that is, that we are the sons of
        God.

1Jo 5:7
5:7 For there are three that bear record in heaven, the Father,
    the {h} Word, and the Holy Ghost: and these three are {i}
    one.

    (h) See  Joh 8:13,14 
    (i) Agree in one.

1Jo 5:9
5:9 {10} If we receive the witness of men, the witness of God is
    greater: for {k} this is the witness of God which he hath
    testified of his Son.

 (10) He shows by an argument of comparison, of what great
      weight the heavenly testimony is, that the Father has
      given of the Son, to whom agrees both the Son himself and
      the Holy Spirit.
    (k) I conclude correctly: for the testimony which I said is
        given in heaven, comes from God, who sets forth his Son.

1Jo 5:10
5:10 {11} He that believeth on the Son of God hath the witness
     in himself: he that believeth not God hath made him a liar;
     because he believeth not the record that God gave of his
     Son.

 (11) He proves the sureness of the earthly witness by every
      man's conscience having that testimony in itself, whose
      conscience he says cannot be deceived because it agrees
      with the heavenly testimony which the Father gives of the
      Son: for otherwise the Father must be a liar, if the
      conscience which agrees and assents to the Father, should
      lie.

1Jo 5:11
5:11 {12} And this is the record, that God hath given to us
     eternal life, and this life is in his Son.

 (12) Now at length he shows what this testimony is that is
      confirmed with so many witnesses: that is, that life or
      everlasting happiness is the gift of God, which is the
      Son, and proceeds from him to us, who by faith are joined
      with him, so that without him, life is nowhere to be
      found.

1Jo 5:13
5:13 {13} These things have I written unto you that believe on
     the name of the Son of God; that ye may know that ye have
     eternal life, and that ye may believe on the name of the
     Son of God.

 (13) The conclusion of the epistle, in which he shows first of
      all, that even they who already believe, need this
      doctrine, that they may grow more and more in faith: that
      is to say, that they may be daily more and more certain of
      their salvation in Christ, through faith.

1Jo 5:14
5:14 {14} And this is the confidence that we have in him, that,
     if we ask any thing according to his will, he heareth us:

 (14) Because we do not yet in effect obtain that which we hope
      for, the apostle combines invocation or prayer with faith,
      which he will have proceed from faith, and moreover to be
      conceived in such a way, that nothing is asked but that
      which is agreeable to the will of God: and such prayers
      cannot be useless.

1Jo 5:16
5:16 {15} If any man see his brother sin a sin [which is] not
     unto death, {l} he shall ask, and he shall give him life
     for them that sin not unto death. There is a sin unto
     death: I do not say that he shall pray for it.

 (15) We have to make prayers not only for ourselves, but also
      for our brothers who sin, that their sins be not to death:
      and yet he excepts that sin which is never forgiven, or
      the sin against the Holy Spirit, that is to say, a
      universal and wilful falling away from the known truth of
      the gospel.
     (l) This is as if he said, let him ask the Lord to forgive
         him, and he will forgive him being so asked.

1Jo 5:17
5:17 {16} All unrighteousness is sin: and there is a sin not
     unto death.

 (16) The taking away of an objection: indeed all iniquity is
      comprehended under the name of sin: but yet we must not
      despair therefore, because every sin is not deadly, and
      without hope of remedy.

1Jo 5:18
5:18 {17} We know that whosoever is born of God sinneth not; but
     he that is begotten of God keepeth himself, and that wicked
     one toucheth him not.

 (17) A reason why not all, or rather why no sin is mortal to
      some: that is, because they are born of God, that is to
      say, made the sons of God in Christ, and being ended with
      his Spirit, they do not serve sin, nor are they mortally
      wounded by Satan.

1Jo 5:19
5:19 {18} [And] we know that we are of God, and the whole world
     lieth in wickedness.

 (18) Every man must particularly apply to himself the general
      promises, that we may certainly persuade ourselves, that
      whereas all the world is by nature lost, we are freely made
      the sons of God, by the sending of Jesus Christ his son to
      us, of whom we are enlightened with the knowledge of the
      true God and everlasting life.

1Jo 5:20
5:20 And we know that the Son of God is come, and hath given us
     an understanding, that we may know him that is true, and we
     are in him that is true, [even] in his Son Jesus Christ.
     This is the true {m} God, and eternal life.

     (m) The divinity of Christ is most clearly proved by this
         passage.

1Jo 5:21
5:21 {19} Little children, keep yourselves from idols. Amen.

 (19) He expresses a plain precept of taking heed of idols:
      which he contrasts with the only true God, that with this
      seal he might seal up all the former doctrine.