That sacred and inviolable bond which unites men of the most discordant opinions into one band of brothers, which gives but one language to men of all nations and one altar to men of all religions, is properly, from the mysterious influence it exerts, denominated the mystic tie; and Freemasons, because they alone are under this influence, or enjoy its benefits, are called "Brethren of the mystic tie."
Popularized by Robert Burns in his farewell to his brethren of St. James Lodge, Tarbolton, Scotland:
Adieu! A heart-warm, fond adieu! Dear Brothers of the Mystic Tie Ye favored, ye enlightened few Companions of my social joy!