And the fifth angel poured out his vial upon the seat of the beast - The previous judgments had been preparatory to this. They all had a bearing on this, and were all preliminary to it; but the “seat” - the home, the center of the power of the beast - had not yet been reached. Here, however, there was a direct blow aimed at that power, still not such yet as to secure its final overthrow, for that is reserved for the pouring out of the last vial, Revelation 16:17-21. All that is represented here is a heavy judgment which was merely preliminary to to that final overthrow, but which affected the very seat of the beast. The phrase “the seat of the beast” - τὸν θρόνον τοῦ θηρίου ton thronon tou thēriou - means the “seat” or “throne” which the representative of that power occupied, the central point of the Anti-christian dominion. Compare the notes on Revelation 13:2. See also Revelation 2:13. I understand this as referring to the very seat of the papal power - Rome - the Vatican.
And his kingdom was full of darkness - Confusion - disorder - distress, for darkness is often the emblem of calamity, Isaiah 59:9-10; Jeremiah 13:16; Ezekiel 30:18; Ezekiel 32:7-8; Ezekiel 34:12; Joel 2:2.
And they gnawed their tongues for pain - This is a “most significant expression of the writhings of anguish.” The word rendered here “gnawed” does not occur elsewhere in the New Testament, nor is the expression elsewhere used in the Bible; but its meaning is plain - it indicates deep anguish.