If MSLN is true, then there is some risk that people will become hardened to the voice of God, and fail to complete coming into tune with him. This could happen, I would think, if a person became an enemy of God consciously, became self-satisfied, became insensitive enough to morality (in that that just is what God wants), became unreceptive to beliefs about God, and perhaps in other cases.
If hardening occurs, it is necessary for people to be destroyed by God, because he can't bear our disharmony forever. Those who are destroyed do not experience eternal life. This is the only source of permanent loss in MSLN, and creates the most pressing moral necessity in it.
There are two possibilities: people are 100% responsible for whether they are hardened ("personal hardening"), or less than 100% responsible (others are also somewhat responsible -- "environmental hardening"). In the latter case, we can be responsible, sometimes, for establishing environments in which other people do not become hardened.
Is it likely enough that MSLN is true, and hardening is possible, and there can be "environmental hardening"? If there is a non-Pascalian nonzero chance of those three things obtaining, then we should employ all sufficiently costless measures to create environments favorable to escaping hardening. If that chance is high enough, we should employ more costly measures, in keeping with its probability.
How can hardening happen? I'm not sure and can't verify this (I don't know if anyone could), so we're left with common sense to forecast.
The theory that I will propose is that we are both tempted and anti-tempted. Our environments offer us the occasion to choose temptation. We either take it, or we don't. If we have fewer occasions, we may be less likely to freely act on them. Each temptation has the chance to move us away from God. There is memory in the process -- previous choices by us create our starting place in a new moment. We might give in, or leap, to temptation. But anti-temptation can work the same way, bringing us back toward God.
If we give in or leap to temptation enough, we can make ourselves enemies of God. Not all temptation is equally dangerous to cause this. But sometimes, in effect, we are tempted to become enemies of God, and if we give in or leap to this, then we are enemies of God, and if this is established enough, we are hardened.
The emphasis on temptation may make it seem like it would be good to cause everyone to have an obviously or outwardly moral life, but hardening is more about no longer having the inner movement toward God. So giving in to anti-temptation may be a better goal or benchmark than not giving in to temptation.
Some temptations are quiet and come with ease. Ease is dangerous. Some temptations are good, at least on some level. (Otherwise God wouldn't allow them in his world.) Getting rid of all temptations is a mixed strategy -- maybe counterproductive. If you got rid of the obvious temptations, you might be left with the temptations of ease. Creating anti-temptations seems like a safe strategy. Anti-temptations help with both a tempting and an easy environment.
A note from a previous draft of this post:
If we do target temptations, it may be best to target those which are most closely connected to hardening: temptations to self-satisfaction, to selling yourself out to an unworthy belief system, to wanting the world to be a certain way in conflict with God, moral desensitization, or a direct enmity with God -- and anything else which we can tell is closely linked with hardening. Another, overlapping, approach would be to say that the most dangerous temptations are those that impede anti-temptation.
If we want to be utilitarians, we might tend to prefer fiducial utilitarianism over hedonic or preferential utilitarianism, because fiducialism is inherently about opening people up and connecting them personally to reality outside themselves, hopefully something that if applied generally opens a door to God among the other doors it opens.
This all makes sense to me rationally, and I think that as far as I can tell right now (January 2021), I see a significant risk of "environmental hardening" being the case, and so it's an area I should do something to help with. But it doesn't make as much sense emotionally or intuitively. It could be that I haven't been raised to have those emotions or intuitions. I was raised in a church where hell was "on the books" but seldom mentioned. People around me rarely if ever seem concerned with the possibility of lostness.
I had a similar emotional / intuitive difficulty believing in a suffering God who negotiates with his spiritual enemies, as you may see here, written in 2017. Now, in 2021, I don't have much trouble "feeling" the truth of it. So I wonder if the same effect may hold here. I haven't thought about this issue much before.