Man does not learn religion as he learns the secrets and mysteries of a trade.

He learns the theory of religion by reflection.

It arises out of the action of his own mind upon the things which he sees, or upon what he may happen to hear or to read, and the practice joins itself thereto.
When men, whether from policy or pious fraud, set up systems of religion incompatible with the word or works of God in the creation, and not only above but repugnant to human comprehension, they were under the necessity of inventing or adopting a word that should serve as a bar to all questions, inquiries and speculations.

The word mystery answered this purpose, and thus it has happened that religion, which is in itself without mystery, has been corrupted into a fog of mysteries.
As mystery answered all general purposes, miracle followed as an occasional auxiliary.

The former served to bewilder the mind, the latter to puzzle the senses.