Some expositors suggest that the angel's proclamation introduces events that are to occur just before Christ’s return (so, in the future). As we see more often, however, the book of Revelation focuses not on the narrow slice of time just before Christ returns, but on the entirety of the new dispensation. The saints of Revelation 14:12 (living as they do in any generation between the time of Christ’s ascension and his return) need repeated and continuous encouragement that they will endure even as they experience attacks from the dragon and its beasts (Revelation 12:1 – 13:18). So they are assured that nations everywhere and at any time may and/or will hear, to Satan’s frustration, God’s eternal gospel.
6 Then I saw another angel flying directly overhead, with an eternal gospel to proclaim to those who dwell on earth, to every nation and tribe and language and people.