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

“‘Who?’ says the Psalmist (and remember that the Psalms were the sacred hymns used in the Hebrew Mysteries), ‘Who will go up to the hill of the Lord, and ascend to His holy place? Even he that hath clean hands and a pure heart’; whence it comes that we wear white gloves and aprons as emblems that we have purified our hearts and washed our hands in innocency.” [via]