Why a Mystery to the unspiritual ecclesiastics of the middle ages

And he answered them, “To you it has been given to know the secrets of the kingdom of heaven, but to them it has not been given. Matthew 13:11 ESV

"The unspiritual ecclesiastics were baffled by the mystic symbolism of
the prophetic books of Daniel and John.

 But this obscurity served as a divinely appointed means of preserving the prophetic word." 

A.G. Daniells