The Bible indicates that there is a sin unto death, which is distinct from other sins and pertains to apostasy from Christ.
The sin unto death, as articulated in 1 John 5:16-21, refers specifically to a grievous transgression that leads to certain death for those who commit it. This sin is often linked to apostasy, a complete turning away from the faith and a rejection of the truth of the Gospel. John Gill describes it as sinning willfully against the Holy Spirit, while John Calvin notes it is not merely a partial fall but a total alienation from Christ. Therefore, when one commits this sin, it reflects a deliberate and doctrinal denial of the faith, and it is understood that nothing can reverse this state, which is why believers are not urged to pray for apostates.
Commentary