This MYSTERY is Babylon.
Rev.17:5 in all capital letters, for effects. It is no mystery for the Election: Babylon is quite obvious. Babylon is a wicked-system, and is upon us.
Mystery - sacred. secret. to conceal. the secret of friends.
Is. 14:4, 14:15 identifies Lucifer as the king of Babylon. It's issues began in the First-Heaven-Age, with the created one, having an Insatiable desire for others to worship It! Lucifer/Satan, 1/3 of the expelled angels, Cain, and his "Generation" and their wicked/rebels have set up shop shop on the earth.
The "Naughty-figs" are controlling their four-kingdoms: education, economics, Politics, and Religion!
Immanuel-Christ-Jesus Commands us -not- to be deceived (Mat24:4). Rom. 12:2 be -not- conformed to this world (chaos).
The MYSTERY, is no mystery to Followers of Immanuel-Christ-Jesus: "see I have told you all things."
Rev.17:8 The beast (Rev.13:4); "and they that dwell on the earth shall wonder (nod),...
Who's in control of miss-education, debt as a currency, worshipping gov. and blind-leaders, and worshipping idols (Religion)???? The MYSTERY, is not.