Matthew Poole and continuators on Revelation 17:8

8 The beast that thou sawest , was , and is not ; and shall ascend out of the bottomless pit , and go into perdition : and they that dwell on the earth shall wonder, whose names are not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is .

This Beast was the Roman Empire, the Scarlet coloured Beast which carried the Whore, v. 3.

Was of old, in Rome's Pagan state,

and is not, not in that form, not now Pagan; and yet is (as is said in the close of the Verse) the same in another form, Idolatrous and Persecuting.

Either out of the Sea, which signifies a multitude of People; or from Hell, (the word signifies both.)

And shall certainly be destroyed.

But before he goes into Perdition he shall so cheat the World, that the generality of the People shall wonder at the Beast (see chap. 13.8.) setting aside those who are chosen of God to Eternal Salvation; the 144000 mentioned chap. 14. I conceive that which hath made Interpreters so divided in their Notions about this Beast is, because those words, and yet is, are not added in the beginning of the Verse, which being understood, there appears no difficulty considerable; for it is certain the Roman Empire was from before Christ, and continued Pagan till 310; then was not Pagan but Christian, yet after some years was again as Idolatrous and Bloody against Christians, as the old Pagan Empire was; especially when swallowed up by the Pope, the Beast with two Horns like a Lamb. This is the Beast with seven Heads and ten Horns, chap. 13.2.

Marginal references: Chap. 13.1.; Chap. 13.10.; Chap. 13.3.