Now this is the state of the souls of the wicked, yea, in darkness, and a state of awful, fearful looking for the fiery indignation of the wrath of God upon them; thus they remain in this state ... until the time of their resurrection (Alma 40:14).
From modern revelation we learn that the expression “endless wo” does not mean that the intended punishment is of endless duration, but rather that it is God’s punishment, and God is endless; therefore he has chosen to call that punishment that comes from him by this name, or endless.
This is done to make the warning more express, “that it might work upon the hearts of the children of men” in the hope that it will dissuade them from sin. (See D&C 19:4-13.)