I previously noted an interesting phenomenon: if you hear from a source that you know with certainty to be infallible, "P is true but you cannot know it," then you'll be thrown into such a state of epistemic confusion that you truly won't know that P, despite having heard it from an infallible source! This suggests that God could undermine or 'defeat' what would otherwise amount to knowledge - and even certain knowledge! - simply by asserting to you that you lack sufficient justification for knowledge. God's assertion here is "self-fulfilling", since it itself is the cause of your epistemic confusion, and is the only reason why your belief fails to constitute knowledge in this case. Speaking generally, we might recognize the phenomenon of "self-fulfilling defeation claims": claims of epistemic defeation in which the claim itself constitutes the defeater. But I'll refer to this phenomenon by the snazzier title of "divine defeation".
Now, I'm wondering just how far God's powers of defeation extend here. (Not that God exists, of course, but it can be a useful philosophical heuristic to pretend otherwise.) His arbitrary proclamations can defeat knowledge, but can they do any more than that? In particular, can they defeat claims of justification, or of high rational subjective probability?
If we stipulate that God cannot utter falsehoods, then he won't be able to say things like, "P is true but you cannot believe it" (for arbitrary P). For that would simply be false; even after hearing God say this, I might go on to believe P (perhaps alongside the second-order belief that I do not believe that P -- hi Moore!). This yields the contradiction that you cannot believe P and you can believe P, thus providing a reductio of the claim that God could utter such a statement.
But what of the divine proclamation, "P is true but you cannot justifiably believe it?" Is this impossible, like the belief case? Or is it instead "self-fulfilling", like the knowledge case? Would hearing such a statement throw a rational agent into such a state of epistemic confusion that they would lose all justification for their belief? That seems implausible to me. You might be confused, but still, testimony from an infallible source has got to count for something, right? If I heard God say that, I would believe that P, and justifiably so! (I might also believe the latter conjunct, i.e. that my former belief is unjustified; but I would simply be mistaken on that point.) So the proclamation would be false, so God could not say it.
The key difference between this and the knowledge case seems to concern the possibility of "meta-defeation". By this I mean the idea that ("meta") doubts about your epistemic status can themselves influence this status. Plausibly, if you doubt whether you know that P, then you actually lack knowledge that P. (This principle seems debatable, however. And if rejected, one might deny that any sort of 'divine defeation' is possible, even for strict knowledge.) But it is far less plausible to hold that such 'meta' considerations defeat justification. One can be justified in believing that P, even if they doubt whether they're so justified.
We could close this gap by building the "meta" considerations into the case. God could say, "P is true, but you cannot justifiably* believe that P (where justification* supplements standard justification with the additional internal requirement that you rationally recognize your belief as being justified)."
Or perhaps that won't work either, since you might believe that P, and recognize this justification ("I heard it from an infallible source!"), all the while mistakenly taking yourself to lack this recognition. That is, much like before, your belief is in fact justified*, even though you don't believe it is justified*. The incongruity is simply pushed back a step. So one-step recursion isn't enough. We're going to need infinite recursion, e.g. by saying: "P is true, but you cannot justifiably** believe that P (where justification** supplements standard justification with the additional internal requirement that you justifiably** recognize your belief as being justified)." If that even makes sense.
(The idea is to close all the "meta" gaps, by rendering it impossible for one to be in this super-justified state without realizing it. In addition to your belief being justified, you must recognize this fact, and also recognize that fact, and then recognize... ad infinitum.)
I'm going to give myself a headache if I go on any further. But it looks like divine defeation is fairly limited in power. Just as well, since I just had an experience as of God telling me that I couldn't justifiably accept the conclusions of this post. That actually isn't true, but you'll never know for sure.