This is the description of our mortal existence. What does it mean to be “lost forever”? Notice that Alma is describing a particular condition. That condition is the expulsion from the Garden and the necessity of death. What Alma has not yet brought into the equation is the Atonement. For this short rhetorical period, Alma is describing a world that is post-Eden, and pre-Atonement. In that particular condition, that of death and no atonement to reconcile death and sin, then men are truly “lost forever” because both death and sin will keep them from their God. They have fallen from God’s presence, and are “lost” to that presence forever (with the big “unless” coming in his next argument).