Revelation 1:20

1:20 The mystery of the seven stars that you saw in my right hand and the seven golden lampstands is this: The seven stars are the angels of the seven churches and the seven lampstands are the seven churches.

Revelation 10:7

10:7 But in the days when the seventh angel is about to blow his trumpet, the mystery of God is completed, just as he has proclaimed to his servants the prophets.”

Revelation 17:7

17:7 But the angel said to me, “Why are you astounded? I will interpret for you the mystery of the woman and of the beast with the seven heads and ten horns that carries her.