The term translated as “must” speaks of divine necessity; that is, God has determined the duration of each king (including, counting from John’s day, how many kings there will be in the future). Though the churches to whom John sends his Revelation (Revelation 1:11) may in time to come experience great hardship on account of the rage of the dragon and his beasts (Revelation 12:17; Revelation 13:1, Revelation 13:7; Revelation 13:15), here the church is assured that the remaining, seventh head of the beast will not last (for the life of a man, even if he is a king, is but a sigh, Psalm 90:5–6). And once the heads are gone, the beast, of course, is gone. Here is the same thought as was expressed in Revelation 17:8: “The beast … go[es] to destruction.”
10 they are also seven kings, five of whom have fallen, one is, the other has not yet come, and when he does come he must remain only a little while.