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

“By perfecting his conduct, by struggles against his own natural propensities, the candidate is working the rough ashlar of his own nature into the perfect cube, and I would ask you to observe also that the cube itself contains a secret, for unfolded, it itself denotes and takes the form of the cross.” [via]