The conditions Alma is describing, post-Eden/pre-atonement, provide two conditions. The first is the ability of “follow after their own will.” This ability is the direct of result of eating the fruit of the Tree of Knowledge of Good and Evil. With the ability to distinguish good and evil, Adam and Eve are now enabled with agency. Their choices may have meaning because they may be associated with the recognition of true choice in their actions.
This benefit of choice had a price, however, which was the possibility of sin. When Alma suggests that it was “not expedient that man should be reclaimed from this temporal death, for that would destroy the great plan of happiness,” he is commenting on the prohibition of eating from the Tree of Life. Of course it will be expedient that there would be an atonement, but he hasn’t got there yet. This is a restatement of the previous argument that Adam and Eve should not have eaten of the fruit of the Tree of Life so that they would live forever in their sins, a condition that will require the atonement.
“To Follow After Their Own Will”
Alma continues to lay out the problem of post-Eden/pre-atonement. The fall from the Garden may have enabled agency, but it also caused physical death, and though sin, the spiritual death of permanent separation from God. In this liminal state in between the fall and the atonement, mankind is “carnal, sensual, and devilish, by nature.” Alma is echoing teachings of Jacob:
2 Nephi 9:6-9
6 For as death hath passed upon all men, to fulfil the merciful plan of the great Creator, there must needs be a power of resurrection, and the resurrection must needs come unto man by reason of the fall; and the fall came by reason of transgression; and because man became fallen they were cut off from the presence of the Lord.
7 Wherefore, it must needs be an infinite atonement—save it should be an infinite atonement this corruption could not put on incorruption. Wherefore, the first judgment which came upon man must needs have remained to an endless duration. And if so, this flesh must have laid down to rot and to crumble to its mother earth, to rise no more.
8 O the wisdom of God, his mercy and grace! For behold, if the flesh should rise no more our spirits must become subject to that angel who fell from before the presence of the Eternal God, and became the devil, to rise no more.
9 And our spirits must have become like unto him, and we become devils, angels to a devil, to be shut out from the presence of our God, and to remain with the father of lies, in misery, like unto himself; yea, to that being who beguiled our first parents, who transformeth himself nigh unto an angel of light, and stirreth up the children of men unto secret combinations of murder and all manner of secret works of darkness.
Jacob tells us that in a condition of sin, without the ability to repent, we are fated to become like the devil. This is the argument that Alma is using for his liminal period where he is attempting to emphasize the need for the atonement by describing what it would be like without it. We are “devilish” by nature during this liminal period for precisely the reasons that Jacob gives – the inability to repent moves us inextricably away from God, and therefore toward the devil.