Question: "What is the sin unto death?"
Answer: 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 seem 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 willful, continuous, unrepentant sin. God has called His children to holiness (1 Peter 1:16), and God corrects them when they sin. We are not “punished” for our sin in the sense of losing salvation or being eternally separated from God, yet we are disciplined. “The Lord disciplines the one he loves, and he chastens everyone he accepts as his son” (Hebrews 12:6).
First John 5:16 says there comes a point when God can no longer allow a believer to continue in unrepentant sin. When that point is reached, God may decide to take the life of the stubbornly sinful believer. The “death” is physical death. God at times purifies His church by removing those who deliberately disobey Him. The apostle John makes a distinction between the “sin that leads to death” and the “sin that does not lead to death.” Not all sin in the church is dealt with the same way because not all sin rises to the level of the “sin that leads to death.”
In Acts 5:1–10 and 1 Corinthians 11:28–32, God dealt with intentional, calculated sin in the church by taking the physical life of the sinner. This is perhaps also what Paul meant by “the destruction of the flesh” in 1 Corinthians 5:5.
John says that we should pray for Christians who are sinning, and that God will hear our prayers. However, there may come a time when God decides to cut short a believer’s life due to unrepentant sin. Prayers for such an unheeding person will not be effective.
God is good and just, and He will eventually make us “a radiant church, without stain or wrinkle or any other blemish, but holy and blameless” (Ephesians 5:27). To further that end, God chastens His children. May the Lord preserve us from the hard-heartedness that would cause us to commit the “sin unto death.”