Alma states his thesis in the first phrase, then repeats it at the end. Fallen humankind must die (because of the expulsion from Eden) and must sin (because of agency). At this point (the interim after Eden but before the atonement), there was no redemption. This position would have been particular vivid because, in fact, Alma and Corianton were living in the interim between the fall and the atonement.
The proper use for this time is repentance, which will remove the barrier of sin between human beings and Yahweh, while awaiting in faith the atonement, which will fully remove sin and also remove physical death.
Alma’s statement that Yahweh would cease to be God if justice were overridden implies that Yahweh recognizes restrictions and that there is at least the possibility that God might not be God. Alma is engaging in hyperbole here; it is absurd (and intended to be absurd) to envision God being capable of being un-God.
The Principle of Eternal Law: A unique and important aspect of LDS theology is the understanding that there are eternal laws and that even God operates within their framework. God’s relationship to those laws is most readily apparent in passages like this one where Alma suggests that God could cease to be God. Two scriptures illuminate this concept:
And if there were miracles wrought then, why has God ceased to be a God of miracles and yet be an unchangeable Being?
And behold, I say unto you he changeth not; if so he would cease to be God; and he ceaseth not to be God, and is a God of miracles. (Morm. 9:19)
This scripture, like Alma 42:13, points out the absurdity of God’s ceasing to be God, yet they both do so by setting up conditions which would deny God his godhood. Mormon tells us that were God to change how he works, then he would cease to be God. Constancy is therefore a critical part of the definition of Godhood.
Alma proposes a different condition. Justice is some kind of eternal constant, the denial of which would cause God to cease to be God. In both cases, godhood is a state, and not a person or persons. God’s children may achieve godhood because there is a way that is part of the same immutable reality as justice. Even God is subject to that reality. This eternal law governs the path of our exaltation:
All kingdoms have a law given;
And there are many kingdoms; for there is no space in the which there is no kingdom; and there is no kingdom in which there is no space, either a greater or a lesser kingdom.
And unto every kingdom is given a law; and unto every law there are certain bounds also and conditions.
All beings who abide not in those conditions are not justified. (D&C 88:36–39)
Regardless of our choices, our rewards are governed by these eternal laws. Doctrine and Covenants 130:120–21 instructs:
There is a law, irrevocably decreed in heaven before the foundations of this world, upon which all blessings are predicated—
And when we obtain any blessing from God, it is by obedience to that law upon which it is predicated.
Our realities operate according to law. Science has discovered many, but many others are revealed to us. Science will never discover those laws, because they pertain to a reality that transcends this earth life, and science is forced by both vision and practice to discover the laws of the universe in which we currently live. Nevertheless, those laws exist and govern even God. They do not limit, but rather enable, God. Obedience and harmony with those eternal laws allow God to be God.