…And the sword of the Spirit, which is the word of God

"…And the sword of the Spirit, which is the word of God:" - Ephesians 6:17 KJV

In this verse, “word” is the Greek “rhema” - an utterance. (Strong’s #G4487).

Thayer’s Greek Lexicon has this to say about the meaning of “word” in Ephesians 6:17:

καθαρίσας... ἐν ῤήματι, according to promise (properly, on the ground of his word of promise, viz. the promise of the pardon of sins; cf.[compare to] Mark 16:16), Ephesians 5:26 (others take ῤήματι here as equivalent to 'the gospel,' cf.[compare to] Ephesians 6:17, Romans 10:8; (see Meyer at the passage));

Thayer’s Greek Lexicon is saying that, in the verses below, others take the Greek word here for “word” as equivalent to ‘the gospel.’

"That he might sanctify and cleanse it with the washing of water by the word, ^G4487" - Ephesians 5:26 KJV

"And take the helmet of salvation, and the sword of the Spirit, which is the word ^G4487 of God:" - Ephesians 6:17 KJV

"But what saith it? The word ^G4487 is nigh thee, even in thy mouth, and in thy heart: that is, the word ^G4487 of faith, which we preach;" - Romans 10:8 KJV

Thayer’s again mentions Ephesians 6:17:

 doctrine, instruction (cf. Winer's Grammar, 123 (117)): (τό) ῤῆμα (τοῦ) Θεοῦ, divine instruction by the preachers of the gospel, Romans 10:17 (R G; but L T Tr WH ῤήματος Χριστοῦ; others give ῤήματος here the sense of command, commission; (cf. Meyer)); saving truth which has God for its author, Ephesians 6:17; also τοῦ κυρίου, 1 Peter 1:25;

The verses mentioned above are:

"So then faith cometh by hearing, and hearing by the word G4487 of God." - Romans 10:17 KJV

"And take the helmet of salvation, and the sword of the Spirit, which is the word G4487 of God:" - Ephesians 6:17 KJV

"But the word G4487 of the Lord endureth for ever. And this is the word G4487 which by the gospel is preached unto you." - 1 Peter 1:25 KJV [And this word is the gospel that was proclaimed to you. (CSB)]

Thus, it appears that the sword of the Spirit, which is the “word” of God, is the gospel.

The gates of hell cannot prevail against it.