I have known people that committed the “sin unto death.” During my 50 years of preaching/teaching the Word of God, many have asked me what this sin is. The Bible says, “If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it. All unrighteousness is sin: and there is a sin not unto death.” (I John 5:16-17)
The Old Testament mentions people who died because of their sin. Nadab and Abihu, the two sons of Aaron the priest, died because they deliberately disobeyed God (Lev. 10:1-7). Korah and his clan opposed God and died (Num. 16). Achan was stoned beccause he disobeyed Joshua’s orders from God at Jericho (Josh. 6-7). Uzzah touched the ark and God killed him (2 Sam. 6).
The New Testament mentions people who died because of their sin. Ananias and Sapphira lied to God about their offering, and they both died (Acts 5:1-11). Some believers at Corinth died because of their actions at the Lord’s Supper (I Cor. 11:30).
If a Christian does not judge, confess, and forsake sin, God chastens him. This process is described in Hebrews 12:1-13, which suggests that a person who does not subject himself to the Father will not live (Hebrews 12:9). In other words, God first “spanks” His rebellious children, and if they do not yield to His will, He may remove them from this world lest their disobedience lead others to sin and bring further shame to His name.
“The sin unto death” is not one specific sin. It is the practicing of a sin with no remorse as the cause of Christ is being hurt. Paul mentioned members of the Church at Corinth who were sickly and some had died because of the unrepentant way they were taking the Lord’s supper. He than said, “For if we would judge ourselves, we should not be judged.” (I Cor. 11:31) If those that had already died because of their sin had simply “judged themselves” or repented, they would not have died prematurely
It is much like a parent’s taking their child to a birthday party. The child sticks his thumb into the birthday cake. The parent takes the child into the bedroom and tells him to act correctly. When they return to the party the child pours a glass of punch on the carpet. The parent takes the child into the bedroom and spanks him. Upon returning to the party, the child pulls the hair of a little girl. The parent finally says, “That’s it! We are going home!” The parent simply takes the rebellious child home.