Dear brothers and sisters, if another believer is overcome by some sin, you who are godly should gently and humbly help that person back onto the right path. And be careful not to fall into the same temptation yourself. Share each other’s burdens, and in this way obey the law of Christ. If you think you are too important to help someone, you are only fooling yourself. You are not that important. (Gal 6:1-3 NLT)
This excludes apostasy. Why? Because apostasy is a knowledgeable turning and rejecting of God once you have met other qualifications. This is talking about being overcome by a sin. The person has grown weak, and somehow fell into sin.
While you are pondering if there is a sin that cannot be restored, ask yourself where you want these people who are in need of restoration. Do you want them excluded from the community? Ridiculed for their sins?
Paul says that he turned some away and out of the congregation not based on sin, but based on doctrinal errors which were disrupting the congregation. Here, he writes about someone needing to be restored.
For those of us who believe that lying is a sin, and we catch someone? Or for those of us who believe that cohabitation? Smoking? Drugs? Alcohol? Homosexuality? Arrogance?
Is restoration limited?