John last saw a woman in the Book of Revelation in chapter 12, where she brought forth the Son of God into the world, then later she went into the wilderness.
The woman was the people of God, first as Israel bringing the Christ into the world, then as the church, producing disciples of Christ.
She goes into the wilderness and disappears for a while, before we see her again in Revelation 17, where we discover that she has changed, but not for the better.
John saw her as a harlot sitting on a beast,
“And on her forehead a name was written: MYSTERY, BABYLON THE GREAT, THE MOTHER OF HARLOTS AND OF THE ABOMINATIONS OF THE EARTH. I saw the woman, drunk with the blood of the saints and with the blood of the martyrs of Jesus. And when I saw her, I marveled with great amazement” (Revelation 17:5-6).
John marveled because it was hard for him to accept what he was seeing. The church had forsaken Christ, although still carrying His name, and claiming allegiance to Him, but she was committing spiritual fornication.
Let us all walk in truth that we may keep the current church pure, and that our congregations do not join in compromise with the world.