So if I understand this correctly, the belief in the divine is rational, not irrational.
In a way, but I think it is deeper than that. Perhaps, that the ideal, that is the transcendental ideal, which could be Divine, if we choose to define it that way, is the
transcendent rational and so is the rationalizer of the rational. So, if there is anything transcendental about the rational, then the very
idea of that thing conditions rationality to it's pinnacle (rather than something like self-consuming "navel-gazing"), not the literal, objectivist existence of an entity such as God.
Here is Scruton on that passage:
Considered thus it is the source, not of illusion, but of knowledge. The knowledge that it leads to remains circumscribed by the conditions of possible experience: in other words, it conforms to the categories, and does not reach beyond their legitimate territory into a transcendent realm. The idea “does not show us how an object is constituted, but how, under its guidance, we should seek to determine the constitution and connection of the objects of experience” (A. 671, B. 699). Thus reason is led back from its vain speculations to the empirical world, trading the illusions of metaphysics for the realities of empirical science.
So, perhaps then it is the manner in which we could connect transcendental rationality to practical, pragmatic rationality.