Q. What does it mean to be faithful during the Tribulation? What must a believer do during the Tribulation so as not to lose the Holy Spirit and his salvation? Will one sin cost a man his salvation? What if he sins and dies immediately? Man sins ever waking moment. Once lost, can they get Him back?
A. All we know is that it means being faithful in the sense that Old Testament believers were faithful. Rev. 14:12 says Tribulation believers have to obey the commandments and remain faithful to Jesus, but the specifics aren’t made clear.
God knows a person’s heart and knows who are His. And He’s not looking for ways to disqualify a person on technicalities. I believe the motive of a person’s heart will still be the major determining factor. As long as he keeps the commandments and maintains his belief that Jesus died for all his sins, I think he’ll be OK. The big difference is that maintaining his faith will be his responsibility. He won’t have the Holy Spirit as a guarantee of his inheritance.