I believe that 1 John epistle was definitely written TO Israel and not to the BODY OF CHRIST .
Hello Dan, if memory serves, John's 1st Epistle is believed to have been authored towards the end of his life (AD 85-90) in the Gentile city of Ephesus (and, no doubt, was first read to the members of his congregation there). If you don't mind me asking, what evidence did you find to the contrary (that this Epistle was meant for Israel alone and not the Church)? Thanks!
As far as whether a believer can still sin or not, it seems to me that 1 John 1-2 tells us that we Christians will continue to struggle with sin throughout the balance of our lives here. The Apostle John makes that especially clear for us, in 1 Jn 1:8 - 2:14, when he includes himself in the mix (along with other believers from all walks/all levels of the faith in the church, from babe to elder in Christ, IOW .. e.g. see v12-14 below) as one who still sinned and, therefore, as one who still needed to be forgiven and cleansed by God of his ongoing sins* on this side of the grave .. 1 John 1:9.
Please take note of the pronouns below in bold.
1 John 1
8 If we say that we have no sin, we are deceiving ourselves and the truth is not in us.
9 If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness.
10 If we say that we have not sinned, we make Him a liar and His word is not in us.
1 John 2
1 My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an Advocate with the Father, Jesus Christ the righteous;
2 and He Himself is the propitiation for our sins; and not for ours only, but also for those of the whole world.
3 By this we know that we have come to know Him, if we keep His commandments.
4 The one who says, “I have come to know Him,” and does not keep His commandments, is a liar, and the truth is not in him;
5 but whoever keeps His word, in him the love of God has truly been perfected. By this we know that we are in Him:
6 the one who says he abides in Him ought himself to walk in the same manner as He walked.
7 Beloved, I am not writing a new commandment to you, but an old commandment which you have had from the beginning; the old commandment is the word which you have heard.
8 On the other hand, I am writing a new commandment to you, which is true in Him and in you, because the darkness is passing away and the true Light is already shining.
9 The one who says he is in the Light and yet hates his brother is in the darkness until now.
10 The one who loves his brother abides in the Light and there is no cause for stumbling in him.
11 But the one who hates his brother is in the darkness and walks in the darkness, and does not know where he is going because the darkness has blinded his eyes.
12 I am writing to you, little children, because your sins have been forgiven you for His name’s sake.
13 I am writing to you, fathers, because you know Him who has been from the beginning. I am writing to you, young men, because you have overcome the evil one. I have written to you, children, because you know the Father.
14 I have written to you, fathers, because you know Him who has been from the beginning. I have written to you, young men, because you are strong, and the word of God abides in you, and you have overcome the evil one.
God bless you!!
--David
p.s. - this is basically a blind post (I just skimmed it quickly), so if this has already been discussed, I apologize. I've gotta go right now, but I hope to return later this evening.
*edit: I thought that I should add that when I spoke of "ongoing" sins above, I was not referring to the continual "practice" of sinning (that of an ongoing, sinful "lifestyle", if you will), because a perpetual, impenitent, sinful lifestyle is some of the best evidence that we have that we/someone else is NOT saved. This kind of sinfulness is, in point of fact, what I believe the Apostle is referring to specifically in 1 John 3:9, for instance.