"In the Christian structure, would it be unlikely that this personal God who is there and made man in his own image as a verbalizer, in such a way that he can communicate horizontally to other men on the basis of propositions and language - is it unthinkable or even surprising that this personal God could or would communicate to man on the basis of propositions?"
Schaeffer offers that he has never met an atheist who thought it a surprise that such a God would or should communicate. Of course, the atheist does not believe that such a God exists to begin with. However, it is quite interesting to think that someone who is being true even to a "what if" scenario should admit that if this God exists, then he would surely be able to communicate with his creatures in very real terms.
While many atheists then would agree with Schaeffer's logical conclusions (though disagreeing on the whole), it seems that many who claim to be theists cannot fathom that this God can or has clearly communicated to his creatures. Beginning at this point of revelation - whether God has truly spoken propositionally to man - is the hinge for most (if not all) other divisions which exist today.