What if you forget one sin ? After all one sin was enough to plunge the whole world into the mess we are in now ? And if Jesus died for all sins that were yet future for you which ones did he leave out and why ?
This question always puzzles me when it's asked because it's doesn't take into account every truth we're taught about the entire process:
1) The sinner is drawn to the Messiah and joins the body through confession (i.e. "I am a sinner..."). All past sins held in forbearance are forgiven. Clean slate. The holy spirit is given. Grace is given. The believer is taught how to walk in The Way.
2) The believer finds themselves in a situation that tempts them to sin, let's say to tempt them to lie...
3) The Holy Spirit speaks to them in their conscience on what they shouldn't do. The choice is now theirs to make...
4) The new believer, not yet exercised or matured, chooses to lie. The situation is over. The sin is committed...
5) The Holy Spirit convicts them with godly sorrow. I.e. they feel bad about it...
6) Feeling a guilty conscience, they immediately find a private place to bend the knee and go before the throne to confess the sin and apologize, receiving their mercy, cleansing, and renewed strength to do better next time.
This is the life of a believer, maturing more and more and sinning less and less.
But if a believer isn't performing step 6, step 5 happens to them less and less until the believer is a follower of the Messiah in name only.
But let's say you can't find a private moment, the day passes, evening comes just before your prayer at night and somehow you forget about your sin. Well there were always offerings for
sins of ignorance even in the OT. And so now after the Messiah your daily prayer includes a confession of sins you committed that you don't recall or were ignorant to, which literally can be saying something like "forgive me of my trespasses today", like the Messiah taught us to pray
daily.
It wouldn't be in the Messiah's model of daily prayer, nor in John's instruction after the cross, if we weren't meant to confess daily. Following a life of daily prayer as believers are expected to do, there's no possible way to miss confessing a sin.
The only way such is possible is if one isn't praying properly each day.
Which ' works salvation ' groups believe that they cleanse there own sins by works, out of interest ?
I'm not sure. I'm not privy to any specific works-based salvation groups. But this was the issue Paul was addressing to the galatians. They were attempting to continue to rituals of cleansing their sins, found in the law, even after the Messiah, when only faith in His work in heaven was now necessary for cleansing sin, after ascension.