With all due respect, CL, I believe you are either (a) being misled or (b) have become confused on these points by dwelling too much on the issue of sin and not enough on the issue of righteousness. There is no such thing as "sin which is dead in us".No, I don't teach sinless perfection. But there are two types of sin, one of which is dead in us because of God indwelling us, and we have no desire to commit, as in 1 John 3:9. It is the context of 1 John 3:4. Those are the sins unto death shown in 1 John 5:16-17.
1. If you are referring to the sin nature within all humans (including Christians), it was nailed to the cross when Christ died for our sins. Which means that "the flesh" (sin nature) no longer has power or dominion over those who have received the gift of the Spirit, and been born again. "Sin shall not have dominion (authority) over you". At the same time, every Christian must (a) reckon himself/herself to be dead to sin and alive to God and (b)mortify or crucify the flesh by denying it the attraction of sin. Temptation and yielding to temptation are not the same thing. We can be tempted but if we refuse to yield we have mortified the flesh.
2. If you are referring to the "sin unto death" that would be any sin in which a Christian persists in spite of all the admonitions of Scripture, or other Christians, or conviction by the Holy Spirit. This kind of sin would result in premature physical death but the soul would be saved. Thus Paul says many "sleep"(die) because of failure to examine themselves.
How can anyone who is walking in the Spirit commit sins? Walking in the Spirit is the exact opposite of walking in the flesh (committing sins).So what about the other? Those we do commit even while walking in the Spirit, but as 1 John 1:7 shows, the blood of Jesus is (automatically and continually) cleansing them - making us appear to God as sinless, if we forgive others the same type of sin who commit them against us.
In any event, what John says is that if we confess our sins, God is faithful and just to forgive us of our sins, and cleanse us from all unrighteousness by the blood of Jesus Christ.
What this means is that if we hold grudges against others and do not forgive them, then God will not forgive our sins either. So we need to examine ourselves and see if we are holding any bitterness or grudges against others.Matthew 6:14-16
14 “For if you forgive men their trespasses, your heavenly Father will also forgive you. 15 But if you do not forgive men their trespasses, neither will your Father forgive your trespasses.