Don't Pray for Person Committing "Sin that Leads to Death"

I'm in a men's Bible study group that meets weekly over breakfast, and we just recently finished studying the epistles of John. We had a good discussion about 1 John 5:16-17 because it basically says to pray for those committing sins that don't lead to death, but don't bother praying for someone in a sin that leads to death.

The "sin that leads to death" is intentional rejection of God even after the person had understood the grace that God offers. We recently read about this in Hebrews (Hebrews 6:4-6). It's also discussed in Matthew 12:31, Mark 3:29, and Luke 12:10. (A good test of whether you are committing this sin is, if you are concerned that you have committed it, you can feel comforted that you haven't--the fact that you care shows you haven't committed it.)

So the Scriptural explanation of this "sin that leads to death" is strong, but what is tricky is the application. How do we know when someone is outright rejecting God? There have been Christians who have turned away from God to embrace sinful lifestyles for many years before repenting.

We determined in our Bible study that here it would be good to "err on the side of grace," meaning if you're not sure, it's better to leave it in God's hands and pray that his will be done and that, if at all possible, he lead that person to repentance. But John does state that if you are sure that someone has outright rejected God for good, there is no need to even pray for them because their sin by its very nature rejects forgiveness.