1st John 5:16-17
1 John 5:16-17 “Suppose you see your brother or sister commit a sin. But that sin is not the kind that leads to death. Then you should pray for them. And God will give life to them. I'm talking about someone whose sin does not lead to death. But there is a sin that does lead to death. I'm not saying that you should pray about that. Every wrong thing we do is sin. But there are sins that do not lead to death.”
The first thing we notice in what might sound like a disturbing passage, is he’s telling us to pray for others – intercessory prayer. It’s very natural for us to pray for someone’s physical healing and it should be just as natural to pray for their spiritual healing.
When we pray like this we must be ready: God may use us as the instrument to help this person. We don’t always just get to drop the ball in God’s lap. Sometimes He tosses it back!
Now the harder part. This passage speaks of the sin whose end is death and the sin whose end is not death. The Jews distinguished 2 kinds of sins. Those committed unwittingly or at least not deliberately; either through complete ignorance or sort of swept away in the moment of some strong emotion.
Then there were the deliberate sins. Knowing full well what you are doing. Some commentaries believe it’s this second type; the deliberate sins that John means because they think that if someone gets away with the sin and doesn’t feel very much remorse they may do it again and feel even less remorseful. And then again and again because it seems like they are getting away with it. And the person goes beyond repentance.
Other commentaries say it's blasphemy; or denying Christ. Not believing He is whom He says He is or repenting and asking for forgiveness of their sins.