What is the sin “unto death” referenced in 1 John 5:16? The cross-references I find are: Num. 15:30 and 16:26-32; 1 Sam 2:25; Jer 15:1-2; Ezek18:34; Matt 12:31-32; Mark 3:28-30; Luke 12:10; 2 Tim 4:14; Heb 6:4-6 and 10:26-31; 2 Peter 2:20-22. For the next verse, a sin “not unto death”, the cross-references are: Isa 1:18; Ezek 18:26-32; Rom 5:20-21; James 1:15 and 4:7-10. The sin “unto death” references sin punishable by death under the law, and presumptuous, deliberate sin; apostacy. Where God’s authority is denied and/or attributed to someone else, it appears to be without remedy (Korah, the Pharisees’ blasphemy against the Holy Spirit). References for the sin “not unto death” are those that are abandoned, covered by Christ’s blood and God’s grace. Is there a sin that cannot be repented of and forgiven? There are a number of interpretations by various Bible scholars, and they don’t necessarily agree. I would love to read what others think about this topic.