A.T. Robertson Commentary Revelation 14:6

"And I saw another angel flying in mid heaven, having eternal good tidings to proclaim unto them that dwell on the earth, and unto every nation and tribe and tongue and people;" — Revelation 14:6 (ASV)

Another angel (αλλον αγγελον). A new turn in the drama comes with each angel (7:2; 8:3,13; 10:1). Here the angel is seen "flying in mid heaven" (πετομενον εν μεσουρανηματ), while in 8:13 John heard him "flying in mid heaven" (genitive case of same participle, which see). This one is in the sight and hearing of all.

Having (εχοντα). Accusative singular agreeing with αγγελον like πετομενον (flying), but λεγων in verse 7 is nominative, as if a new sentence like λεγων in 4:1.

An eternal gospel (ευαγγελιον αιωνιον). The only use of ευαγγελιον in John's writings, though the verb ευαγγελισα (first aorist active infinitive epexegetical with εχοντα like Joh 16:12) occurs here and in 10:7. Here it is not το ευαγγελιον (the gospel), but merely a proclamation of God's eternal (αιωνιος here alone in the Apocalypse, though common in the Fourth Gospel and I John) purpose. Origen even took this "eternal gospel" to be another book to be written! Note the double use of επ (with accusative after ευαγγελισα and the genitive with γης). See 5:9 for the races, etc.