Who or What is the Whore of Babylon? #Revelation #Endtimes #LastDays

Revelation 17 introduces readers to the 'whore of Babylon,' a wicked entity who rides on the back of the beast, causes Kings of the earth to commit immorality with her, and is drunk with the blood of the saints that she has killed. Who is the frightening entity, and what does the 'Babylon' in her title refer to?