I'm somewhat tentatively of the opinion that "1 John", like "To the Hebrews" was not written to "Christians" but rather to new covenant Jews. The only writings in the scriptures that are written specifically to Christians (which I'm distinguishing as the "body of Christ", Paul's "new creation") are the letters that Paul wrote (Romans to Philemon). Obviously "To the Hebrews" was written to the Hebrews. Peter and James both explicitly address their letters to "the 12 tribes" and "the diaspora". The believing Jews in 1 John had a different relationship and different salvation from those to whom Paul wrote. They were Jews living in the last days of the Israel-centered "kingdom program" of the previous dispensation (before the "church age" that Paul introduced). Please bear with me a few minutes...
First of all, 1 John appeals to John's first hand knowledge of the earthly Jesus:
1Jn 1:1 That which was from the beginning, which we have heard, which
we have seen with our eyes, which we have looked upon, and our hands
have handled, of the Word of life; 1Jn 1:2 (For the life was
manifested, and we have seen it, and bear witness, and shew unto you
that eternal life, which was with the Father, and was manifested unto
us;) 1Jn 1:3 That which we have seen and heard declare we unto you,
that ye also may have fellowship with us: and truly our fellowship is
with the Father, and with his Son Jesus Christ.
But Paul did was not a disciple of the earthly Christ:
2Co 5:16 Wherefore henceforth know we no man after the flesh: yea,
though we have known Christ after the flesh, yet now henceforth know
we him no more.
The earthly Jesus was a Jew, made of the seed of David, born under the law:
Gal_4:4 But when the fulness of the time was come, God sent forth his
Son, made of a woman, made under the law,
The new covenant was not in effect while he was alive:
Heb_9:16 For where a testament is, there must also of necessity be
the death of the testator. Heb_9:17 For a testament is of force after
men are dead: otherwise it is of no strength at all while the testator
Jesus taught the law and a works salvation:
Luk_18:20 Thou knowest the commandments, Do not commit adultery, Do
not kill, Do not steal, Do not bear false witness, Honour thy father
and thy mother.
So also does 1 John:
1Jn_2:3 And hereby we do know that we know him, if we keep his
commandments. 1Jn_2:4 He that saith, I know him, and keepeth not his
commandments, is a liar, and the truth is not in him.
1Jn_3:22 And whatsoever we ask, we receive of him, because we keep
his commandments, and do those things that are pleasing in his sight.
1Jn_3:24 And he that keepeth his commandments dwelleth in him, and he
in him. And hereby we know that he abideth in us, by the Spirit which
he hath given us.
1Jn_5:2 By this we know that we love the children of God, when we
love God, and keep his commandments. 1Jn_5:3 For this is the love of
God, that we keep his commandments: and his commandments are not
Sin in 1 John is transgression of the law (and vice versa):
1Jn 3:4 Whosoever committeth sin transgresseth also the law: for sin
is the transgression of the law.
Paul clearly distinguishes sinning under the law from sinning apart from the law:
Rom 5:12 Wherefore, as by one man sin entered into the world, and
death by sin; and so death passed upon all men, for that all have
sinned: Rom 5:13 (For until the law sin was in the world: but sin
is not imputed when there is no law. Rom 5:14 Nevertheless death
reigned from Adam to Moses, even over them that had not sinned after
the similitude of Adam's transgression, who is the figure of him that
was to come.
For the disciples of the earthly Jesus (Jews, as Jews, believing in Jesus' messiahship prior to 70AD) justification was not an accomplished work given freely by grace but one that involved being "rewashed" from every sin in dependence on a heavenly priest and advocate:
1Jn 1:7 But if we walk in the light, as he is in the light, we have
fellowship one with another, and the blood of Jesus Christ his Son
cleanseth us from all sin. 1Jn 1:8 If we say that we have no sin, we
deceive ourselves, and the truth is not in us. 1Jn 1:9 If we confess
our sins, he is faithful and just to forgive us our sins, and to
cleanse us from all unrighteousness.
The one who hopes to be saved must "overcome" by the maintenance of their lives in purity and righteous living:
1Jn 2:28 And now, little children, abide in him; that, when he shall
appear, we may have confidence, and not be ashamed before him at his
coming. 1Jn 2:29 If ye know that he is righteous, ye know that every
one that doeth righteousness is born of him.
1Jn 3:3 And every man that hath this hope in him purifieth himself,
even as he is pure. 1Jn 3:4 Whosoever committeth sin transgresseth
also the law: for sin is the transgression of the law. 1Jn 3:5 And
ye know that he was manifested to take away our sins; and in him is no
sin. 1Jn 3:6 Whosoever abideth in him sinneth not: whosoever sinneth
hath not seen him, neither known him. 1Jn 3:7 Little children, let
no man deceive you: he that doeth righteousness is righteous, even as
he is righteous. 1Jn 3:8 He that committeth sin is of the devil; for
the devil sinneth from the beginning. For this purpose the Son of God
was manifested, that he might destroy the works of the devil. 1Jn
3:9 Whosoever is born of God doth not commit sin; for his seed
remaineth in him: and he cannot sin, because he is born of God. 1Jn
3:10 In this the children of God are manifest, and the children of
the devil: whosoever doeth not righteousness is not of God, neither he
that loveth not his brother.
But in the dispensation of grace that God brought through Paul justification is a gift received based on the obedience of a single man, Jesus:
Rom_5:19 For as by one man's disobedience many were made sinners, so
by the obedience of one shall many be made righteous.
So I don't count myself to be among the audience of 1 John as it was written specifically to the Jews who acknowledged Jesus as their messiah but lived prior to (or still outside of) Paul's "new man", the "body of Christ". Paul is my apostle because he was the apostle to the gentiles and to him was given the dispensation of the grace of God and it was he who was made the architect of the new man.
I said at the outset that I was tentative about his audience being Jews under the new covenant. I believe that to be the case but since he doesn't mention the new covenant (as "To the Hebrews" clearly does) I am cautious about it. However he does seem to so draw a line between sinners who are not born of God and do not have his character and those that are born and do have his character it appears that he is writing to those who have God's law written on their hearts and who experience the promise of the forgiveness of sins under that covenant:
1Jn 3:5 And ye know that he was manifested to take away our sins; and
in him is no sin. 1Jn 3:6 Whosoever abideth in him sinneth not:
whosoever sinneth hath not seen him, neither known him. 1Jn 3:7
Little children, let no man deceive you: he that doeth righteousness
is righteous, even as he is righteous. 1Jn 3:8 He that committeth
sin is of the devil; for the devil sinneth from the beginning. For
this purpose the Son of God was manifested, that he might destroy the
works of the devil. 1Jn 3:9 Whosoever is born of God doth not commit
sin; for his seed remaineth in him: and he cannot sin, because he is
born of God. 1Jn 3:10 In this the children of God are manifest, and
the children of the devil: whosoever doeth not righteousness is not of
God, neither he that loveth not his brother.
KJV unless otherwise noted.