Revelation 16:14 (Morphology and Syntax)

Greek (WH): εἰσὶν γὰρ πνεύματα δαιμονίων ποιοῦντα σημεῖα, ἃ ἐκπορεύεται ἐπὶ τοὺς βασιλεῖς τῆς οἰκουμένης ὅλης, συναγαγεῖν αὐτοὺς εἰς τὸν πόλεμον τῆς ἡμέρας τῆς μεγάλης τοῦ θεοῦ τοῦ παντοκράτορος.

NET Bible: For they are the spirits of the demons performing signs who go out to the kings of the earth to bring them together for the battle that will take place on the great day of God, the All-Powerful.

εἰσὶν is the present active indicative 3rd person plural of εἰμί ("they are")

γὰρ is a conjunction, here translated "for."

Smyth: γάρ (postpositive) in fact, indeed , and for, a confirmatory adverb and a causal conjunction. As a conjunction, γάρ usually stands after the first word in its clause; as an adverb, its position is freer. γάρ is especially common in sentences which offer a reason for, or an explanation of, a preceding or following statement. It may be used in successive clauses.

See http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0007%3Apart%3D4%3Achapter%3D60%3Asection%3D182

As noted in a previous entry, some understand the genitival construction πνεύματα δαιμονίων to be epexegetical ("spirits who are demons") whereas others insist it's adjectival or descriptive ("demonic spirits").

See https://fosterheologicalreflections.blogspot.com/2021/12/revelation-1613-frogs-and-spirits.html?showComment=1639558193983#c6831231754791705526

ποιοῦντα σημεῖα ("performing signs")-present active participle modifying an accusative plural neuter noun. In this context, the participle is best understood as "to perform" or "carry out." Compare Revelation 13:13-14.

ἃ ἐκπορεύεται ἐπὶ τοὺς βασιλεῖς τῆς οἰκουμένης ὅλης ("who go forth to the kings of the whole inhabited earth")-Compare Revelation 3:10; 12:9. The conflict will be global, not merely confined to one area.

A.T. Robertson renders "which go forth" and he observes that Revelation 16:14 contains a
"Singular verb with neuter plural (collective) subject."

συναγαγεῖν αὐτοὺς εἰς τὸν πόλεμον τῆς ἡμέρας τῆς μεγάλης ("to gather them together for the war of the great day")-Robertson thinks the aorist active infinitive συναγαγεῖν expresses the unclean spirits' purpose. It answers why the signs go forth to the earth's kings.

The day of YHWH (Jehovah) is a prominent Hebrew Bible theme (Joel 2:11, 31; Obadiah 15-16; Zephaniah 1:14; Malachi 4:5).

τοῦ θεοῦ τοῦ παντοκράτορος-("of God the Almighty")-Translation note from NET:

tn On this word BDAG 755 s.v. παντοκράτωρ states, “the Almighty, All-Powerful, Omnipotent (One) only of God…(ὁ) κύριος ὁ θεὸς ὁ π.…Rv 1:8; 4:8; 11:17; 15:3; 16:7; 21:22.”

Robert Mounce (The Book of Revelation in the NICNT Series): "The first clause of v. 14 is a parenthetical remark that explains why the spirits are called evil. 'They are diabolical spirits performing wonders' (Phillips). The following clause ('and they go
out') connects with 'three evil spirits' of v. 13 and completes the sentence that began, 'Then I saw.' John’s syntax invites considerable conjecture at times."