A.T. Robertson Commentary Revelation 20:8

"and shall come forth to deceive the nations which are in the four corners of the earth, Gog and Magog, to gather them together to the war: the number of whom is as the sand of the sea." — Revelation 20:8 (ASV)

To deceive the nations (πλανησα τα εθνη). First aorist active infinitive of purpose of πλαναω, Satan's chief task (chapters 12 to 18, in particular 12:9; 13:14; 19:20; 20:3,10).

Which are in the four corners of the earth (τα εν ταις τεσσαρσ γωνιαις της γης). Clearly the reign with Christ, if on earth, was not shared in by all on earth, for Satan finds a large and ready following on his release. See 7:1 (Isaiah 11:12) for "the four corners of the earth."

Gog and Magog (τον Γωγ κα Μαγωγ). Accusative in explanatory apposition with τα εθνη (the nations). Magog is first mentioned in Ge 10:2. The reference here seems to be Eze 38:2, where both are mentioned. Josephus (Ant. I. 6. 1) identifies Magog with the Scythians, with Gog as their prince. In the rabbinical writings Gog and Magog appear as the enemies of the Messiah. Some early Christian writers thought of the Goths and Huns, but Augustine refuses to narrow the imagery and sees only the final protest of the world against Christianity.

To gather them together to the war (συναγαγειν αυτους εις τον πολεμον). Second aorist active infinitive of purpose of συναγω, a congenial task for Satan after his confinement. See 16:14 for this very phrase and also 17:14; 19:19.

Of whom (ων--αυτων). Pleonasm or redundant pronoun as in 3:8 and often (of whom, of them).

As the sand of the sea (ως η αμμος της θαλασσης). Already in 12:18. Clearly then the millennium, whatever it is, does not mean a period when Satan has no following on earth, for this vast host rallies at once to his standard.