Considering John says 'we', does that mean John was not a Christian?
1 John 1:8 If WE say WE have no sin, we deceive ourselves, and the truth is not in us
Of course not. He is talking to his congregation, thus "we." Not everyone in his congregation were Christians. However, the use of first person is common practice in Semitic writing styles to include a broader base.
Paul did the same thing in Romans 7, another use of first person that westerners conclude he is speaking of himself. But in Romans 7:9 was Paul even alive when mankind received the law on Mt. Sinai? "9 I was alive once without the law, but when the commandment came, sin revived and I died."
1 John 1:8 is the same sentiment as Paul's "all have sinned and fallen short of the glory of God." He is talking since Adam sinned. But Who can save us from sin? Jesus. When reading 1 John 1:8 it is best reading it in context. There is a before and after sense to the verse then and what John is actually meaning, even though his wording points directly against Gnosticism who really did not believe their sins of the flesh were
sin. Thirteen or more translations of the Bible start the next verse with the word, "but" tying them together.
"If we say that we have no sin, we deceive ourselves, and the truth is not in us. 9 But, if we confess our sins, He is faithful and just to forgive us
our sins and to cleanse us from
all unrighteousness."
Think about it. If you are cleansed of all filth are you still dirty? This is why a true Christian is no longer a sinner, but a saint. It is important to tell yourself the truth, for most of our behavior stems from what we believe. This is why in Romans 6, Paul tells us a
fact - we are
dead to sin. But later in the same chapter tells us to also
reckon ourselves dead to sin. Why? Isn't it still a fact? Yes, but we have free will, and there is power in our thoughts. Don't hide away the fact in your closet. Therefore Paul also says,
But
put on the Lord Jesus Christ, and make no provision for the flesh, to
fulfill its lusts.
and that you
put on the new man which was created according to God, in true righteousness and holiness.
Put on the whole armor of God, that you may be able to stand against the wiles of the devil.
We have been given righteousness, but not over filth as a cover-up, as was true with the blood of bulls and goats; but over a cleansed heart and mind that has been washed clean by the blood of Jesus that takes away sin, not just covers it up. Do not stir up the flesh and resurrect it, when you've been given a new nature that loves righteousness.
The bottom line is, the person who is walking in the Spirit, does not have uncleansed sin in their life. You don't commit willful, presumptuous sin which is lawlessness, and the trespasses you commit are automatically cleansed per 1 John 1:7. So don't quench the Spirit.
Of course, this is all based on the premise that the person professing to be a Christian, actually is one - they have the Spirit of Christ empowering them to not commit willful/presumptuous sin. In other words, a liar or con-artist is not a Christian. Nor any committing these sins of the flesh in Galatians 5:19-21.