Revelation 17 introduces us to the great harlot. She stands in contrast to the woman of the wilderness from Revelation 12. Her dominion is on the many waters; she rules over “peoples, multitudes, nations, and tongues” (Rev. 17:1, 15). These men are intoxicated with her and all she has to offer.
She sits on the beast (Rev. 13:1). There is great luxury and opulence with her (gold, precious stones, etc.), but she is desolate (wilderness). The cup in her hand is gold, very appealing, but full of abominations (toxic). This is a perfect description of Rome. Its material wealth and world domination intoxicated men, but her moral and spiritual bankruptcy proved her ultimately harmful.
This woman on the beast appears very appealing, but is revealed to be a harlot (Rev. 17:5); and is drunk with the blood of the saints. Rome was involved in the ruthless persecution of Christians.
This harlot (Rome) has characteristics of many ancient harlots. She was a harlot of conquest and destruction like Nineveh (Nah. 3:1, 4). She was similar to Tyre, the harlot of commerce (Isa. 23:15-17). Pleasure was a top pursuit, just like Babylon (Isa. 47:8, 9). She was also analogous to the great spiritual harlot, Israel (Isa. 1:21). All of these abhorrent features were found in first-century Rome. Therefore, she is condemned by God.
In Revelation 17:7-18, the angel explains the vision.
Lust controls the beast and the beast upholds the lust (Rev. 17:7, 9).
The seven heads, mountains, and kings are the power aligned against Christ (Rev. 17:9-11).
The ten kings are lesser kings who compromise with the beast (Rev. 17:12, 13).
The Lamb will win (Rev. 17:14).
The waters are people of the earth (Rev. 17:15-17; cf. Dan. 2:40-43).
The woman is specifically identified as “that great city;” lust, seduction, allurements of the flesh (Rev. 17:18).
Looking back it is easy to see how all of this fits Rome. Remember, the letter of Revelation was written to Christians in the first century. Its primary application was to them, not us. Just like 1 Corinthians was written to the church at Corinth and was first pertinent to them. We can learn from these letters, but let us be careful with Revelation in trying to make it primarily applicable to present-day events.
Back to the point: Kings of the earth compromised many things to curry the favor of the Roman Empire. These forces, driven by their worldly lusts, stood opposed to Jesus Christ and His Kingdom. Hence, there was a great battle taking place. It appeared that they were winning. Christians (those of the seven churches and others) were concerned that their cause would fail. This letter was written to let them know the Lamb, Jesus, would be victorious over this satanic power. All who were with Him would gain the victory too—they just had to remain faithful.