A.T. Robertson Commentary Revelation 4:1

"After these things I saw, and behold, a door opened in heaven, and the first voice that I heard, [a voice] as of a trumpet speaking with me, one saying, Come up hither, and I will show thee the things which must come to pass hereafter." — Revelation 4:1 (ASV)

After these things (μετα ταυτα). Change in the panorama, not chronology (7:1,9; 15:5; 18:1; 19:1). This vision is of heaven, not of earth as was true of chapters Re 1; 2. The first vision of Christ and the messages to the seven churches began in 1:12f. This new vision of the throne in heaven (4:1-11) succeeds that to which it here alludes.

I saw (ειδον). Second aorist active indicative of οραω.

Behold (ιδου). Exclamation of vivid emotion as John looked. No effect on the structure and nominative case θυρα (door) follows it.

Opened (ηνεωιγμενη). Perfect (triple reduplication) passive participle of ανοιγω as in 3:8 (door of opportunity) and 3:20 (door of the heart), here the door of revelation (Swete).

In heaven (εν τω ουρανω). As in Eze 1:1; Mr 1:10; John 1:51. In Revelation always in singular except 12:12.

The first (η πρωτη). Reference is to 1:10.

Speaking (λαλουσης). From λαλεω, rather λεγουσης of 1:10 from λεγω, both agreeing with σαλπιγγος (trumpet).

Saying (λεγων). Present active participle of λεγω repeating the idea of λαλουσης, but in the nominative masculine singular construed with φωνη (feminine singular), construction according to sense because of the person behind the voice as in 11:15; 19:14.

Come up (αναβα). Short Koine form for αναβηθ (second aorist active imperative second person singular of αναβαινω).

Hither (ωδε). Originally "here," but vernacular use (John 6:25; John 10:27).

I will show (δειξω). Future active of δεικνυμ in same sense in 1:1.

Hereafter (μετα ταυτα). Some editors (Westcott and Hort) connect these words with the beginning of verse 2.