The unknown can be interpreted in different ways, when we project our subjective reactions onto it which say more about us than the unknown. But much that's subversive follows from acknowledging that the Source is unknowable.

Egoism, for example, becomes vain as we're humbled by the limits of our knowledge. Pessimism about our mental projections follows, too, as well as the elitist distinction implied in your comment that "not everyone can accept it in all its terror." Some defer to the metaphors and mental projections, while the more philosophical individuals see through them and thus can't trust in them.

The Source's unknowability entails atheism, of course, which undermines theology as a whole in so far as theology requires the god metaphor.

One question, then, is what sort of religion can support a negative, mystical theology. Leo Strauss would say the ordinary kind of religion works with this paradoxical knowledge, but only cynically because the exoteric conceptions are used by the elites to reassure the terrified or clueless masses, while the philosophical insiders are jaded about egoism, society, theology, and everything else in relation to that great unknown. (Think of the skepticism of Ecclesiastes.) The philosophical/spiritual elites become the Machiavellian leaders familiar from politics.