Understand that, in Revelation 18:4, God is not calling on the world to repent from their sins and convert to Christian (Messianic) Judaism. 'My people' in the verse implies that they already believe in Jesus God except that they are at the wrong place.
What do those who believe in Jesus God do?
Those who believe in Jesus go to church or to synagogue. Therefore, if they are called upon to come out, it implies necessarily that the churches, the synagogues are Babylon which the serious believers in Jesus must come out of.
Hence, Babylon is Christianity and Protestantism.
THE APOCALYPTIC CLUES WHICH IDENTIFY THE MYSTERIOUS PROSTITUTE BABYLON THE MEGA
Revelation 17:1 ESV
Then one of the seven angels who had the seven bowls came and said to me, “Come, I will show you the judgment of the great prostitute who is seated on many waters,
Revelation 17:15 ASV
(15) And he saith unto me, The waters which thou sawest, where the harlot sitteth, are peoples, and multitudes, and nations, and tongues.
Revelation 17:4-5 ASV
(4) And the woman was arrayed in purple and scarlet, and decked with gold and precious stone and pearls, having in her hand a golden cup full of abominations, even the unclean things of her fornication, (5) and upon her forehead a name written, MYSTERY, BABYLON THE GREAT, THE MOTHER OF THE HARLOTS AND OF THE ABOMINATIONS OF THE EARTH.
Deuteronomy 31:16 ASV
And Jehovah said unto Moses, Behold, thou shalt sleep with thy fathers; and this people will rise up, and play the harlot after the strange gods of the land, whither they go to be among them, and will forsake me, and break my covenant which I have made with them.
Leviticus 20:3-7 ASV
(3) I also will set my face against that man, and will cut him off from among his people; because he hath given of his seed unto Molech, to defile my sanctuary, and to profane my holy name.
(4) And if the people at the land do at all hide their eyes from that man, when he giveth of his seed unto Molech, and put him not to death;
(5) then I will set my face against that man, and against his family, and will cut him off, and all that play the harlot after him, to play the harlot with Molech, from among their people.
(6) And the soul that turneth unto them that have familiar spirits, and unto the wizards, to play the harlot after them, I will even set my face against that soul, and will cut him off from among his people.
(7) Sanctify yourselves therefore, and be ye holy; for I am Jehovah your God.
Numbers 25:1-5 DRB
(1) And Israel at that time abode in Settim, and the people committed fornication with the daughters of Moab,
(2) Who called them to their sacrifices. And they ate of them, and adored their gods.
(3) And Israel was initiated to Beelphegor: upon which the Lord being angry,
(4) Said to Moses: Take all the princes of the people, and hang them up on gibbets against the sun: that my fury may be turned away from Israel.
(5) And Moses said to the judges of Israel: Let every man kill his neighbours, that have been initiated to Beelphegor.
What is an abomination in Judaism? Unlawful sexual relations like as listed in Leviticus chapter 18: homosexuality in Lev 18:22, 20:13; consuming unclean meat, fowl, seafood in Deuteronomy chapter 14:1-21 because we are holy (verse 2), child sacrifice in Deuteronomy 12:31, 18:10, idolatry or worship of graven images of silver or of Gold Deuteronomy 7:25-26, in Isaiah 41:24; more than abomination like bestiality in Leviticus 18:23 and sex with daughter-in-law (Leviticus 20:12), false prophets who teach the worship of idols in Deuteronomy chapter 13; divination or witchcraft and its forms in Deuteronomy 18:9-14, swingers (wide fellowship or joining in group), spiritism, necromancer in Deuteronomy 18:11. Read those aforementioned chapters.
Revelation 17:6 DRB
And I saw the woman drunk with the blood of the saints and with the blood of the martyrs of Jesus. And I wondered, when I had seen her, with great admiration.
Revelation 18:24 DRB
And in her was found the blood of prophets and of saints and of all that were slain upon the earth.
Revelation 17:18 ASV
And the woman whom thou sawest is the great city, which reigneth over the kings of the earth.
Revelation 18:10 ASV
standing afar off for the fear of her torment, saying, Woe, woe, the great city, Babylon, the strong city! for in one hour is thy judgment come.
Revelation 18:17 ASV
for in one hour so great riches is made desolate. And every shipmaster, and every one that saileth any whither, and mariners, and as many as gain their living by sea, stood afar off,
Revelation 18:4 ASV
(4) And I heard another voice from heaven, saying, Come forth, my people, out of her, that ye have no fellowship with her sins, and that ye receive not of her plagues:
Babylon, is made up of more than one church (harlot) because she is the mother of churches who break with Judaism in one doctrine or another. Each child of Babylon carries one doctrine of disobedience or disagreement of Satan, the disguised messenger of light (2 Corinthians 11:13-15).
and upon her forehead a name written, MYSTERY, BABYLON THE GREAT, THE MOTHER OF THE HARLOTS AND OF THE ABOMINATIONS OF THE EARTH. Revelation 17:5 ASV
Does your church disagree with Moses and the Prophets (Judaism) in one doctrine (Luke 16:27-31)? If yes, your denomination is a child or a harlot of mother Babylon.