The Deeper Symbolism of Freemasonry from The Meaning of Masonry by Walter Leslie Wilmshurst.

“We know that even the elementary and superficial secrets of the Order must not be communicated to unqualified persons, and the reason for this injunction is not so much because those secrets have any special value, but because that silence is intended to be typical of that which applies to the greater, deeper secrets, some of which, for appropriate reasons, must not be communicated, and some of which indeed are not communicable at all, because they transcend the power of communication.” [via]