John Calvin says, "I have already said that the sin to which there is no hope of pardon left, is thus called. But it may be asked, what this is; for it must be very atrocious, when God thus so severely punishes it. It may be gathered from the context, that it is not, as they say, a partial fall, or a transgression of a single commandment, but apostasy, by which men wholly alienate themselves from God. For the Apostle afterwards adds, that the children of God do not sin, that is, that they do not forsake God, and wholly surrender themselves to Satan, to be his slaves. Such a defection, it is no wonder that it is mortal; for God never thus deprives his own people of the grace of the Spirit; but they ever retain some spark of true religion.
|The Apostle John|
It is commonly held that John is referring to the blasphemy of the Holy Spirit (Matthew 12:31). And I grant that is a plausible interpretation, because it is the only sin described in Scripture for which there is no forgiveness. I could see Calvin's interpretation in this case. However, I'm not sure that solves our problem, because Jesus didn't explain what constitutes blasphemy against the Holy Spirit, yet it is something that John considers discernible to his audience. Furthermore, since John was present when Jesus made that declaration, why didn't he use the words of Jesus, if that is the sin that he meant? So, while I agree that this interpretation is possible, I do not see it as probable.
My personal opinion is that John is referring neither to ultimate apostasy nor the blasphemy of the Holy Spirit (which are probably the same thing). Rather, I think he means those sins that make the perpetrator subject to capital punishment, such as murder. That is, John expects Christians to support the godly social order, not to expect God to undermine lawful justice. he is repeating a concept of Moses's: "If a man has committed a crime punishable by death and he is put to death, and you hang him on a tree, his body shall not remain all night on the tree, but you shall bury him the same day, for a hanged man is cursed by God. You shall not defile your land that the Lord your God is giving you for an inheritance" (Deuteronomy 21:22-23). That land is polluted by the tolerance of heinous wickedness, and it is the responsibility of the godly man to work for, and to maintain, God's justice as the means of removing that pollution.