To show that the sorer punishment that he has spoken of is real, the writer quotes from Deuteronomy 32:35-36: ‘To me belongeth vengeance, and recompense; their foot shall slide in due time: for the day of their calamity is at hand, and the things that shall come upon them make haste. For the LORD shall judge his people, and repent himself for his servants, when he seeth that their power is gone, and there is none shut up, or left.
How will the Lord judge his people? In the context of Deuteronomy 32, we are thinking of Israel as a mixed multitude of believers and unbelievers. The judgment referred to is one which separates the true from the false. The passage does not teach that God’s true people will have to face a judgment at the end of life for their sins: Christ has already taken the full punishment for all our sins and God will not punish them twice. It teaches that there are those who are not true believers but who masquerade as such among the people of God. Among the readers of this letter there may also have been those who lacked faith and who were about to depart from the church. But others would have a glimpse into the destiny of the apostates and recoil from the sin of unbelief.