Rev 17:1 And there came one of the seven angels which had the seven vials, and talked with me, saying unto me, Come hither; I will show unto thee the judgment of the great whore that sitteth upon many waters:
Rev 17:2 With whom the kings of the earth have committed fornication, and the inhabitants of the earth have been made drunk with the wine of her fornication.
This was spiritual idolatry. According to religious history and legend, the Babylonian religion was founded by the wife of Nimrod (a great-grandson of Noah), named Semiramis. She was a high priestess of idol worship, and she gave birth to a son who she claimed was conceived miraculously. The son, named Tammuz, was considered a savior. Many ancient artifacts remain with the familiar motif of the mother Semiramis holding the savior-infant Tammuz, which predate Christianity. It was also said that Tammuz was killed by a wild beast and then miraculously brought back to life. Baal was the local, Canaanite name for the Babylonian Tammuz. (Guzik)
Satan brought about a false religion, of worshipping gods, goddesses and even a false Christ, such as Tammuz. This is the great spiritual harlot, the world's false religions.
Ezek 8:14 Then he brought me to the door of the gate of the LORD'S house which was toward the north; and, behold, there sat women weeping for Tammuz.
Ezek 8:15 Then said he unto me, Hast thou seen this, O son of man? turn thee yet again, and thou shalt see greater abominations than these.
Queen of heaven idolotry
Jer 7:18 The children gather wood, and the fathers kindle the fire, and the women knead their dough, to make cakes to the queen of heaven, and to pour out drink offerings unto other gods, that they may provoke me to anger.
Jer 7:19 Do they provoke me to anger? saith the LORD: do they not provoke themselves to the confusion of their own faces?
Rev 17:3 So he carried me away in the spirit into the wilderness: and I saw a woman sit upon a scarlet coloured beast, full of names of blasphemy, having seven heads and ten horns.
Rev 12:3 And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads.
The woman sat upon the dragon, satan, who was full of blaspheme and his representative ruler, the antichrist, who crawled out of the sea of humanity, himself filled with satan.
Rev 13:1 And I stood upon the sand of the sea, and saw a beast rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy.
Rev 13:2 And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and great authority.
Rev 17:4 And the woman was arrayed in purple and scarlet colour, and decked with gold and precious stones and pearls, having a golden cup in her hand full of abominations and filthiness of her fornication:
Purple and scarlet were very costly garments, worn only by rulers and people of power. The woman represents all the false worship and ceremonies of the antichrist religions. The faith was not of God.
2 Tim 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
Rev 17:5 And upon her forehead was a name written, MYSTERY, BABYLON THE GREAT, THE MOTHER OF HARLOTS AND ABOMINATIONS OF THE EARTH.
Mystery Babylon, spiritual Babylon, the mother of harlots, of false beliefs, of idolatry and abominations of the earth.