John had previously seen two signs,
first of a woman (Revelation 12:1) and then of a great red dragon (Revelation 12:3). John had witnessed the conflict between those two entities, specifically how the dragon sought to devour the child the woman bore but was frustrated in his attempt (Revelation 12:4–5) and how the dragon subsequently went to make war on the woman’s offspring (Revelation 12:17) and enlisted the help of evil beasts from sea (Revelation 13:1) and land (Revelation 13:11) to accomplish his goals. Though the full number of the elect would eventually all be gathered on Mount Zion (Revelation 14:1), God’s announcement of justice (Revelation 14:10, Revelation 14:19) remained unfulfilled. The present sign connects to the previous two signs as prophecy to fulfillment.
1 Then I saw another sign in heaven, great and amazing, seven angels with seven plagues, which are the last, for with them the wrath of God is finished.