A.T. Robertson Commentary Revelation 8:13

"And I saw, and I heard an eagle, flying in mid heaven, saying with a great voice, Woe, woe, woe, for them that dwell on the earth, by reason of the other voices of the trumpet of the three angels, who are yet to sound." — Revelation 8:13 (ASV)

An eagle (ενος αετου). "One eagle," perhaps ενος (εις) used as an indefinite article (9:13; 18:21; 19:17). See 4:7 also for the flying eagle, the strongest of birds, sometimes a symbol of vengeance (Deuteronomy 28:49; Hosea 8:1; Habakkuk 1:8).

Flying in mid-heaven (πετομενου εν μεσουρανηματ). Like the angel in 14:6 and the birds in 19:17. Μεσουρανημα (from μεσουρανεω to be in mid-heaven) is a late word (Plutarch, papyri) for the sun at noon, in N.T. only these three examples. This eagle is flying where all can see, and crying so that all can hear.

Woe, woe, woe (ουαι, ουαι, ουα). Triple because three trumpets yet to come. In 18:10,16,19 the double ουα is merely for emphasis.

For them that dwell on the earth (τους κατοικουντας). Accusative of the articular present active participle of κατοικεω, is unusual (Aleph Q here and also in 12:12) as in Mt 11:21. There is even a nominative in 18:10.

By reason of the other voices (εκ των λοιπων φωνων). "As a result of (εκ) the rest of the voices." There is more and worse to come, "of the three angels who are yet to sound" (των τριων αγγελων των μελλοντων σαλπιζειν).