1 John 5:16-17
16 If you see any brother or sister commit a sin that does not lead to death, you should pray and God will give them life. I refer to those whose sin does not lead to death. There is a sin that leads to death. I am not saying that you should pray about that. 17 All wrongdoing is sin, and there is sin that does not lead to death.
This saying about "a sin that leads to death" is difficult to interpret. Here are some of the alternatives given by well known theologians.
1. This is similar to the sin of the "blaspheme of the Holy Spirit" that Jesus mentions in Mark 3:28-30
"Truly I tell you, all sins and blasphemes will be forgiven for the sons of men. But whoever blasphemes against the Holy Spirit will never be forgiven, but is guilty of an eternal sin. He said this because they [the Pharisees] were saying, 'He has an evil spirit'." Blaspheming the Holy Spirit would be to call something of the Holy Spirit and attribute it to evil.
2. Others refer to the story Ananias and Sapphira in Acts 5, when they sell a piece of property and hold back some of the property to themselves, while appearing to lay it at the disciples feet. Here is what Peter says to Ananias at the time,
“Ananias, how is it that Satan has so filled your heart that you have lied to the Holy Spirit and have kept for yourself some of the money you received for the land? 4 Didn’t it belong to you before it was sold? And after it was sold, wasn’t the money at your disposal? What made you think of doing such a thing? You have not lied just to human beings but to God.” 5 When Ananias heard this, he fell down and died."
3. Paul refers to something similar when he is trying to correct the abuses in Corinthian church, regarding how they were practicing the Lord's Supper. He says in 1 Corinthians 11,
"27 So then, whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord. 28 Everyone ought to examine themselves before they eat of the bread and drink from the cup. 29 For those who eat and drink without discerning the body of Christ eat and drink judgment on themselves. 30 That is why many among you are weak and sick, and a number of you have fallen asleep. 31 But if we were more discerning with regard to ourselves, we would not come under such judgment. 32 Nevertheless, when we are judged in this way by the Lord, we are being disciplined so that we will not be finally condemned with the world."
All 3 of these texts are also troublesome to bible commentators. Why? Didn't Jesus come to forgive us of our sin not condemn us? How do we know if we are holding back something from God, and how serious does it have to be to receive Ananias and Sapphira's fate? Do we blaspheme the Holy Spirit when we attribute things to God that we shouldn't? How do we not fall into the error of receiving Holy Communion in manner unworthy of The Lord? Is this when we really don't confess our sin when taking communion? You can see how this could become problematic in the life of faith.
And how does this relate to what 1 John writes about the "sin that leads to death"? While the instances above might seem logical as ways to interpret this difficult passage, I am going to make a different argument. And I go back to the foremost principle of biblical interpretation, which is context. Who is the author? Who is he writing to? What is his purpose? We know John's purpose is that he is writing to the early church to warn them of false teachers. He calls them "anti-Christs". And they are teaching that Jesus wasn't really a man, he just looked like man. Their sin is different in that they are teaching something that leads others into sin and away from Christ. They deny the very aspects of who Jesus is that make him capable of forgiving our sin. The sin of false teaching always leads to death, because it denies the only One who can lead us to life, and life everlasting.
So John says there is is kind of sin that leads to death, but that is not what I am referring to. I am referring to sin that is going to happen in the community of faith, when people disobey God's commands. These are the sins we pray for each other and confess to each other. So while we need to take sin seriously and confess it to God and others, we don't have to be in fear of condemnation. Paul says in Romans 8:1, "There is therefore no condemnation for those who are in Christ Jesus!"