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

“And hence also it is that the Lodge has seven principal officers, and that a Lodge, to be perfect, requires the presence of seven brethren; though the deeper meaning of this phrase is that the individual man, in virtue of his seven-fold constitution, in himself constitutes the ‘perfect Lodge,’ if he will but know himself and analyse his own nature aright.” [via]