What sin does God not forgive?
The one sin God does not forgive is unbelief—refusing to believe that Christ died for them, paid their sin debt, and rose from the dead. Even the vilest immorality can be forgiven, but persistent unbelief seals that person's own doom.
Les explains that Israel's sin with the golden calf was vile, but God could forgive that kind of sin. Their real problem was unbelief—they could not believe what He said. Quoting Hebrews, Les notes they could not enter His rest because of unbelief. He emphasizes nothing has changed: God can forgive to the uttermost any sin, the vilest of sin, except one—unbelief. When people refuse to believe that Christ died for them, paid their sin debt, and rose from the dead in power, their doom is sealed. All He asks is that they believe it.