'Mystery' in the Bible

The mystery of the seven stars which thou hast seen on my right hand, and the seven golden lamps. The seven stars are angels of the seven assemblies; and the seven lamps are seven assemblies.

but in the days of the voice of the seventh angel, when he is about to sound the trumpet, the mystery of God also shall be completed, as he has made known the glad tidings to his own bondmen the prophets.

and upon her forehead a name written, Mystery, great Babylon, the mother of the harlots, and of the abominations of the earth.

And the angel said to me, Why hast thou wondered? I will tell thee the mystery of the woman, and of the beast which carries her, which has the seven heads and the ten horns.