Alma 42:9

therefore, as the soul could never die, and the fall had brought upon all mankind a spiritual death as well as a temporal; that is, they were cut off from the presence of the Lord; therefore it was expedient that mankind should be reclaimed from this spiritual death;

The soul can never die. The fall brought spiritual death to all people, not just physical death. They were cut off from the Lord. So people needed to be saved from this spiritual death.

The soul lives forever, and the fall brought spiritual death on everyone, not just physical death. We were cut off from the Lord’s presence. So it was necessary for humanity to be rescued from this spiritual death.