What is the “sin unto death” in 1 John 5:16? I have been told it refers to believers who cross the line and God takes them home.
The sin that leads to death is the refusal to believe Jesus died for all our sins. John was writing against the Gnostic error which among other things taught that it wasn’t the death of Jesus that allowed us to be forgiven for our sins. Instead it was the acquisition of secret knowledge. Believing this leads to death because it puts us outside the only provision God has made for our forgiveness. Scientology, Freemasonry, and other false religions are based on this same idea.
The Lord’s death paid the penalty for all the sins of our life, and He forgave us for every one of them when He went to the cross (Colossians 2:13-14). Since all of our sins are already forgiven the idea that we could somehow commit a sin bad enough that it would cause God to end our life and take us to heaven is not Biblical, but is a man made notion.
Besides it doesn’t make sense that the consequences for committing such a terrible sin would be an early arrival in Heaven where we’ll live in a state of unimaginable bliss forever. It’s like getting a head start on eternity for being bad.