Sin that Leads to Death

Question

What is the "sin that leads to death" (1 John 5:16)? Why does John say that "there is sin that does not lead to death" when Paul clearly says that "the wages of [presumably all] sin is death" (Rom. 6:23)?

Answer

On the issue of sins that do and don't lead to death, in my estimation Paul and John may be speaking of different kinds of death. Paul is speaking of eternal death as a spiritual state (in contrast to eternal life [Rom. 6:23]). John, however, may be speaking merely of the physical death of the body (cf. James 5:14-16). Also, whereas Paul speaks of sin that leads to death for the unbeliever, John appears to be speaking of sin that leads to death for a "brother," one who, short of evidence to the contrary, is assumed to be saved. When believers sin, our sins do not lead to death because we are forgiven in our advocate Christ (e.g. Rom. 8:34; 1 John 2:1-2). Even if John is speaking of eternal death, his point may be that Christians ought not to pray for a so-called brothers who reveal that they are unsaved and without hope of salvation (i.e. via blasphemy of the Holy Spirit).