What does 'mystery' (mysterion) mean in Revelation 17?

When Revelation 17:5 stamps the word mysterion (μυστήριον, G3466, "mystery") on the forehead of the woman called "Babylon the Great," it's doing something specific and consistent with how the word functions throughout the book. Every time mysterion appears in Revelation, it signals that a symbolic image is about to be decoded. The seven stars are a mystery — then the angel explains they are the seven churches (Rev 1:20). The mystery of God will be finished at the seventh trumpet (Rev 10:7). In Revelation 17, the name "Babylon" itself is the mystery — a cipher whose meaning the angel is about to unpack.

The angel makes this explicit in the very next verse: "I will tell you the mystery of the woman and of the beast that carries her" (Rev 17:7). The word mysterion isn't blocking the reader from knowing what Babylon means — it's announcing that the name is a symbol pointing to something beyond the ruined city on the Euphrates, and the explanation is coming.

Then the angel delivers six explicit interpretations within the vision itself. The many waters are peoples, multitudes, nations, and languages (Rev 17:15). The seven heads are seven mountains where the woman sits, and also seven kings (Rev 17:9–10). The beast is an eighth king from among the seven, heading to destruction (Rev 17:11). The ten horns are ten kings who receive power for one hour with the beast (Rev 17:12). And the woman is "the great city that has dominion over the kings of the earth" (Rev 17:18).

The mysterion label is the reader's instruction manual: begin with what the text decodes directly, move to what it implies, only then reach for inference. Six things are decoded right there in the passage. The study works through what those six decodings tell us, and what remains genuinely unresolved. For the full analysis, see Mystery Babylon.