First John 5:16 is one of the most difficult verses in the New Testament to interpret. “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. I am not saying that he should pray about that.” Of all the interpretations out there, none seems to answer all the questions concerning this verse. The best interpretation may be found by comparing this verse to what happened to Ananias and Sapphira in Acts 5:1-10 (see also 1 Corinthians 11:30). The “sin unto death” is deliberate, willful, continuous, unrepentant sin. God, in His grace, allows His children to sin without immediately punishing them. However, there comes a point when God will no longer allow a believer to continue in unrepentant sin. When this point is reached, God sometimes decides to punish a Christian, even to the point of taking his or her life.
That is what He did in Acts 5:1-10 and 1 Corinthians 11:28-32. This is perhaps what Paul described to the Corinthian church in 1 Corinthians 5:1-5. We are to pray for Christians who are sinning. However, there may come a time when God will no longer hear prayers for a sinning believer for whom He has determined that judgment is due. It is difficult to realize there are times when it is just too late to pray for a person. God is good and just, and we will just have to let Him decide when it is too late.