This past week we took a look at the 1st epistle of John, chapter 5. In that chapter John writes: "If anyone sees his brother commit a sin that does not lead to death, he should pray and God will give him life. I refer to those whose sin does not lead to death. There is a sin that leads to death."
Now the natural question from John's statement is, "What sin leads to death and which sin doesn't?" Because if I am going to commit a sin, let it be the later (the non-death one).
Three theories have been suggested (and since John does not give details about which sin is which, we can only assume that the people he was writing to knew the difference.)
1. Moses' sin- These would be sins that Moses, in writing the inspired law, would have said were sins whose punishment was death. For instance, murder. In Genesis 9:6 we read this, "Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image." In Leviticus 24:17 we read this, "Whoever takes a human life shall surely be put to death." So the sin of murder would bring about your own death.
2. Apostasy- this would be turning away from God and denying the faith. The sin of apostasy would lead to spiritual ruin and a spiritual death, much like we see in the Cain and Able story. Such a death would cause a rejection from a relationship with God.
3. Heretical Sin- This would be spreading false narratives about God and causing others to fall into a false belief. As the author of such sin, you would be held responsible for that, and, as Jesus said, it would be better to have a millstone tied around your next and to be thrown into the lake.
Since John is discussing number three to the people he wrote to in his letter, some commentators have stated that John is saying that the sin of spreading false information and causing others to follow a heretical path leads to your death. I would tend to agree.