Here’s an excerpt of an email I sent a couple of years back to someone on this same topic.
The beautiful thing (from my perspective and abstracting from practical matters) is that this lack of public verifiability of spiritual things is actually a necessary condition for diametrically opposed worldviews. On the one hand are worldviews that assert that spiritual things are largely irrelevant – because they don’t exist. On the other hand is the worldview that claims that spiritual things are of primary relevance in this estate because they constitute the primary dimension in which we demonstrate our fitness for greater opportunities in [a future state]. Non-verifiability of spiritual experiences (and therefore spiritual truth generally) is implied in each case: in one case because they don’t exist, and in the other because indiscriminate (i.e. public) verifiability would largely destroy the purpose of this mortal experience by limiting our ability to choose what to believe and consequently how to act towards ourselves and towards one another. Now, because this condition (no public verifiability of what’s spiritual) is necessary for both of those worldviews, it is uninformative regarding which one actually obtains (i.e. it cannot be legitimately used to eliminate one or the other from the set of viable explanations of what we observe regarding public verifiability) - and this is precisely as it should be. This means that a priori assignment of spiritual matters to the domain of irrelevance without honest and thorough experimentation is ultimately not only unscientific (why not follow the gospel invitations [e.g. explicitly provided in Alma 32 or by the missionaries] to carry out the experiments at the personal level and see for oneself?) but also somewhat disingenuous it seems, from a purely conceptual standpoint.[3]
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Perhaps not surprisingly, a similar situation (involving extremes) arises where the principle of natural selection is concerned: there are indeed different – in some ways even diametrically opposed - “selection” criteria (e.g. the “usual” one exhibited in the animal kingdom, and the one suggested in DC121, the last third of 2NE26, and elsewhere in the scriptures); but how very different are their corresponding outcomes for the behavior and the happiness of both the individual and the group! Is it any wonder that we learn that sociality will be “there” like it is “here”? We will have each chosen our reality in some senses - including the kinds of associations we’ll be comfortable in: telestial, terrestrial, or celestial. I suspect that some may be taken in their own craftiness on this one - after the manner described by DC121:12. What a terrible surprise it may end up being for some to find that the same principle they used to justify becoming selfish/egocentric individuals in [mortality] has become the operative principle by which they are deemed unfit for greater opportunities and influence … in the hereafter (DC 121). After the environmental phase-transition precipitated by mortal death, it may become absolutely clear that the kinds of character traits advantageous for mortal-physical survival may in many cases stand in direct conflict with those required to rule in glory and dominion – and “without compulsory means”! It appears to be the case that great power and selfishness or capriciousness are fundamentally incompatible, or at least unsustainable in the long run – perhaps due to the existence and agency of uncountably many other intelligences (who could “gang up”) or to the tendency for self-deception that seems to accompany selfishness.[4] Shadows of just such principles show up throughout the histories of past civilizations (in and out of the scriptures), but without much notice by a world obsessed with the next episode of “Friends” or “Seinfeld” (or whatever other false gods we choose to worship/emulate).
[2] Distinguishing between the two is useful because it is standard practice in the world, even if it turns out that the two kinds of truth are more similar than most people are willing to grant. For example, the restored gospel suggests (e.g. Alma 32) that experimentation – including exercising faith, patience, and diligence along the way – is just as necessary for learning spiritual as for “scientific” truths, even if verification of those experiments is necessarily individual – as opposed to public – in nature. Likewise, Joseph Smith’s description of the process of revelation has a similar experimental/inductive flavor.
[3] To cut some well-intentioned critics some slack, they generally operate without any exposure to the revelatory updates of recent centuries – including expanded (though always geared at developing the spiritual matrix that is most important) descriptions of the “beginning” of this world, and explicit recognition of infinitely many others. Perhaps as a consequence of this and of confusing spiritual truth with historical religions, some people I’ve met seem to accept evolutionary artifacts as prima facie evidence against spiritual things. But in reality all claimed inconsistencies between the two (the actual artifacts – not the theories – and faith) are largely contrived.
[4] Knowledge of all types accumulates more slowly for self-deceivers I would guess; and there is a way in which knowledge is power (as the saying goes). Besides, Godel showed with his incompleteness theorem that the subset of truth accessible by rational/empirical processes may ultimately be quite limited, leaving room for that other epistemological pillar: revelation of truth from a source that knows what rational process cannot access.