The final punishment was death in the wilderness. There was no reprieve, no suspension of sentence; they were simply not leaving the midbar. For every other sin, Hashem forgave them. When they rebelled with the Golden Calf, He forgave them. When they complained for no reason, Hashem forgave them. When they sinned when they followed Korach in contesting Moshe and Aharon’s leadership, Hashem forgave them. The only sin for which there was no room for forgiveness was the chet ha’meraglim, sin of the spies. They slandered; they were punished. Why? They cried that night, a weeping that was called a bechiah shel chinam, weeping for nothing. We have been compensated with a bechiah l’doros, weeping for generations, with Tisha B’Av, our day commemorating national tragedy. Until Moshiach arrives, we will weep. Hashem will not forgive us. Why?
Horav Yitzchak Elchanan Spektor, zl, makes a profound observation. We derive from here that for all sins there is penance. There are sins between man and G-d and sins between man and his fellowman. Hashem forgives these sins after the proper teshuvah, repentance, has been effected. When one sins against his nation, when the sinner is a traitor to his people, there is no room for forgiveness. “In the wilderness shall they cease to be, and there shall they die.” We should remember this lesson.