 The sin that leads to death, is he referring to the unpardonable sin of blaspheming in the Holy Spirit? Or is he referring to a believer who continues to live in sin and God just finally says, okay, you're not listening. I'm going to take you out of this world. Maybe he was speaking to both. Either one of them actually fit the context of the passage. In my humble opinion, if you choose a spiritual understanding for it, I don't think you're wrong.