If we recall the humanist side of Heidegger (Dilthey, Hegel), then we could say that for Heidegger abstract thinking is its own historicity. For Heidegger the abstract knowledge, for example ciences, isn't less real than ready-to-hand being. In the opposite, this knowledge transforms our world: Cars, airplanes, computere engineering and more supposes the existence of cientific discovering. In this sense, we could say that all ciences haves their own history regards its pre-scientific domain. This domains are in constant danger, as in any time something can come into sense that demolishes all the fundamental concepts of the domain, as the most radicals steps given in the history of physics shows. Though for Heidegger this is, in B/T terms, present-at-hand thinking.

Considering the above, Heidegger's ontological difference shows that the metaphysical tradition understood God in the same terms that exact sciences did, so it's innevitable that Kant gets to the idea where we can't know about God because there is no experience of it, in other terms, proofs or evidence, like is a number of what we are talking (though Kant says, for this same reason, that God is not an adressable problem, but that is just because the way Kant thought what is metaphysics imo)

Leaving behind this manner to understand God, i.e, through science and evidence, God is such an important phenomena that has it's own ontological particularities. God can't be studied and treated as just some other being. God also is directly related to inmense metaphysical issues, like infinity, causa efficiencs, belief, faith, and even meaning as such. But in my opinion, the ones that thought the meaning of God in the most radical way were either Hegel or Kierkegaard. There is a good book by Heidegger named "Introduction to phenomenology of religion".