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

“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?” [via]