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

“Brethren, I charge you to regard your apron as one of the most precious and speaking symbols our Order has to give you.” [via]

Consider also:

  1. “In some Masonic Lodges the candidate makes his first entrance to the Lodge room amid the clash of swords and the sounds of strife, to intimate to him that he is leaving the confusion and jarring of the religious sects of the exterior world, and is passing into a Temple wherein the Brethren dwell together in unity of thought in regard to the basal truths of life, truths which can permit of no difference or schism.”
  2. “Yet, there exists a large number of brethren who would willingly repair this obvious deficiency, brethren to whose natures Masonry, even in the more limited aspect of it, makes a profound appeal and who feel their membership of the Craft to be privilege which has brought them into the presence of something greater than they know, and that enshrines a purpose and that could unfold a message deeper than they at present realize.”
  3. “It is well to emphasize then, at the outset, that Masonry is a sacramental system possessing, like all sacraments, an outward and visible side consisting; of its ceremonial, its doctrine and its symbols which we can see and hear, and an inward, intellectual, and spiritual side, which is concealed behind the ceremonial, the doctrine and the symbols, and which is available only to the Mason who has learned to use his spiritual imagination and who can appreciate the reality that lies behind the veil of outward symbol.”
  4. “Anyone, of course, can understand the simpler meaning of our symbols, especially with the help of the explanatory lectures; but he may still miss the meaning of the scheme as a vital whole.”
  5. “But upon entering this world, the soul must needs assume material form; in other words it takes upon itself a physical body to enable it to enter into relations with the physical world, and to perform the functions appropriate to it in this particular phase of its career. Need I say that the physical form with which we have all been invested by the Creator upon our entrance into this world, and of which we shall all divest ourselves when we leave the Lodge of this life, is represented among us by our Masonic apron?”