Some people believe that Mystery Babylon the Great is located in the Vatican City in Rome, home of the Roman Catholic religion and some believe Mystery Babylon will be located in Mecca, home of the Sunni Islam religion.  However, the Lord said the following in Rev. 18:4:

Rev. 18:4, "And I heard another voice from heaven, saying, Come out of her, my people, that ye be not partakers of her sins, and that ye receive not of her plagues."

(Who are are "my people" who are the Lord's people that He wants to come out of Mystery Babylon? The two verses below in 2 Chronicles 7:14 and 2 Corin. 6:16 show that "my people" are Christians that are called by the Lord's name Christ.)

2 Chronicles 7:14, "If my people, which are called by my name, shall humble themselves, and pray, and seek my face, and turn from their wicked ways; then will I hear from heaven, and will forgive their sin, and will heal their land."

2 Corin. 6:16, "And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people."

(In regards to Mystery Babylon in verse Rev. 18:7 below, Mystery Babylon says I sit a queen and am no widow and shall see no sorrow.  The reason why Mystery Babylon thinks she is a queen is because she mistakenly believes she is the Bride of Christ who is espoused to the Lord Jesus Christ, King of Kings. She thinks she is no widow because He is very much alive unlike Muhammed of the Islam religion who died in 632 A.D.)

Rev. 18:7, "How much she hath glorified herself, and lived deliciously, so much torment and sorrow give her: for she saith in her heart, I sit a queen, and am no widow, and shall see no sorrow."

(What Mystery Babylon represents is Apostate Christianity of all the apostate churches with Satan and the future Antichrist as its head which is why the Lord wants the apostate Christians to come out of Apostate Christianity now and to repent and turn from their wicked ways.)

(And once any apostate Christian worships the Antichrist and the image of the Beast (his image) and takes his mark in the right hand or in the forehead, it will be impossible to come out of Mystery Babylon as their fate is sealed according to Rev. 14:9-11; and when they worship the Antichrist and his image they will also be worshipping Satan, the dragon, himself according to Rev. 13:4 below:)

Rev. 13:4, "And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?"

Exodus 20:3, "Thou shalt have no other gods before me."