The nostics believed "they" never sin, but their body does and this was a popular teaching going around back in the Apostle John's time which is why he taught against it in the little John books.
So gnosticism is tied to bodily sinning with spiritual purity. I guess it takes a whole lot of hard mind work to come up with that.

And even more Bible tampering to make it stick theologically.
Honestly, I have never seen so many volumes of words and explanations to say someone's religion doesn't depend on how they live.
Exactly.Now days, calvinists and reformed theology peoples have put forth various versions of OSAS which is teaching the idea that once can live in sin and not lose their salvation which is not only not biblical but is a stumbling block of other believers causing many to fall way from the Lord.
But shun profane and vain babblings: for they will increase unto more ungodliness.
It actually keeps themselves fallen away from the righteousness of the Lord, while keeping themselves saved by the Lord.
It's so simple to know a Christian is sticking to the Bible to teach the doctrine of Christ.Which should result in Christians who rarely ever sin and if they did it's not a situation where they knew something was sinful and decided to go ahead and do it anyway.
It's as simple as saying 'if' we sin. 'If' being the all important operative word.
Christians who speak of when they sin, have set themselves entirely apart from Bible doctrine of Christ.
Thanks much.