Alma highlights the problem. In this condition, the expulsion from Eden so that they must die, and the exercise of agency whereby the were fated to sin through choice, there was no hope. There was no redemption at this point. Now Alma begins to work his way to the next phase of the argument. He begins to show this as an interim time period. Again we have the analogy to the time between death and resurrection. Alma is using the symbolic time between the expulsion from the Garden and the atonement as model for earth life. This is particularly appropriate for Alma because they conceptually found themselves in precisely that condition. They were living in that interim time between the Fall and the atonement. Thus Alma is describing the way that they see their own time. They are in the conditions of the Fall, and awaiting the resolution of that state through the coming atonement.
What Alma suggests is that this liminal period is useful, and it is useful for repentance. The spiritual separation of man from God comes through man’s sins. Thus repentance and turning away from sin will at least remove that barrier from the man (awaiting the atonement for the full removal of the sin before God).
One of Alma’s statements is interesting. He suggests that if justice were destroyed, God would cease to be God. This is a remarkable statement because it suggests that God has restrictions placed upon him, and that there is at least a conceivable state in which God might not be God. Of course Alma’s point is that this is an absurd possibility, surely God would not, could not do anything so un-Godlike, but the point still suggests that the nature of God is absolute.
The Principle of Eternal Law: One of the unique and important aspects of LDS theology is the understanding that there are eternal laws, and that even God operates within the framework of these eternal laws. The relationship of God to those laws is most readily seen in verses such as this where Alma suggests that there might be a way in which god would cease to be God. To understand this principle, we turn to two different scriptural texts:
Mormon 9:19
19 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.
And for easier reference, the verse under current consideration:
Alma 42:13
13 Therefore, according to justice, the plan of redemption could not be brought about, only on conditions of repentance of men in this probationary state, yea, this preparatory state; for except it were for these conditions, mercy could not take effect except it should destroy the work of justice. Now the work of justice could not be destroyed; if so, God would cease to be God.
Clearly the intent of these scriptures is to point out how unreasonable it would be for God to cease to be God. Yet the both do so in a way in which certain conditions are set up which would deny God His Godhood. Mormon tells us that were God to change (that is change in the way he works - not in the sense of progression) that He would cease to be God. The constancy of action is somehow a critical part of the definition of Godhood.
Alma, on the other hand, has a different possibility. For Alma, Justice is some kind of Eternally Real constant, and to violate the demands of justice would cause God to cease to be God. In both cases, it underlines the issue that Godhood is a state, and not a person or persons. The state of Godhood may be achieved by the children of God because there is a Way. That Way is part of the immutable Reality. It is a Reality to which even God is subject. This eternal law governs the path of our celestialization.
Doctrine and Covenants 88:34-39
36 All kingdoms have a law given;
37 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.
38 And unto every kingdom is given a law; and unto every law there are certain bounds also and conditions.
39 All beings who abide not in those conditions are not justified.
Regardless of the choices we make, our rewards are governed by aspects of the eternal laws.
The Doctrine and Covenants instructs us that: “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”. DC 130:20-21. All of our known reality operates under various laws. There are many that science has discovered, such as laws of gravity and motion. There are many others that are revealed to us. Science will never discover those laws, because they pertain to a reality that transcends this earth life, and science if forced by both vision and practice to discover the laws of the universe in which we currently live. Nevertheless, those laws exist, and are laws that govern even God. They do not limit God, but rather enable God. Obedience and harmony with those eternal laws is what allows God to be God.