In Greek, there are two words for sword, μάχαιρα, machaira, and ῥομφαία, rhomphaia. The primary difference between the two is size. A machaira is a large knife or small sword. A rhomphaia is larger and usually attached to a pole. Typically each would have a only single edge so describing either as "two-edged" is unusual.
1,2There are four passages to consider:
and take the helmet of salvation, and the sword of the Spirit, which is the word of God
(Ephesians 6:17 ESV)
καὶ τὴν περικεφαλαίαν τοῦ σωτηρίου δέξασθε καὶ τὴν μάχαιραν τοῦ πνεύματος ὅ ἐστιν ῥῆμα θεοῦ
For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart. (Hebrews 4:12)
ζῶν γὰρ ὁ λόγος τοῦ θεοῦ καὶ ἐνεργὴς καὶ τομώτερος ὑπὲρ πᾶσαν μάχαιραν δίστομον καὶ διϊκνούμενος ἄχρι μερισμοῦ ψυχῆς καὶ πνεύματος ἁρμῶν τε καὶ μυελῶν καὶ κριτικὸς ἐνθυμήσεων καὶ ἐννοιῶν καρδίας
In his right hand he held seven stars, from his mouth came a sharp two-edged sword, and his face was like the sun shining in full strength. (Revelation 1:16)
καὶ ἔχων ἐν τῇ δεξιᾷ χειρὶ αὐτοῦ ἀστέρας ἑπτά καὶ ἐκ τοῦ στόματος αὐτοῦ ῥομφαία δίστομος ὀξεῖα ἐκπορευομένη καὶ ἡ ὄψις αὐτοῦ ὡς ὁ ἥλιος φαίνει ἐν τῇ δυνάμει αὐτοῦ
“And to the angel of the church in Pergamum write: ‘The words of him who has the sharp two-edged sword. (Revelation 2:12)
καὶ τῷ ἀγγέλῳ τῆς ἐν Περγάμῳ ἐκκλησίας γράψον τάδε λέγει ὁ ἔχων τὴν ῥομφαίαν τὴν δίστομον τὴν ὀξεῖαν
When used with sword, there are two types of word: ῥῆμα, rhema, and λόγος, logos. Therefore, the passage in Hebrews has common elements with those in Revelation (and not with Ephesians):
Type Characteristic Word of God
Ephesians 6:17 macharia of the Spirit rhema
Hebrews 4:12 macharia two-edged logos
Revelation 1:16 rhomphaia sharp two-edged logos
Revelation 2:12 rhomphaia sharp two-edged logos
In his commentary on Revelation, Gerald L. Stevens notes the connection between the two-edged rhomphaia in Revelation and the two-edged macharia in Hebrews:
Mouth: sharp, two-edged sword (1:16), martial imagery allusive of war, but "out of the mouth" means not a normal war. Rather, this is a war of words, of witness and testimony. Sword imagery in biblical contexts normally implies a word of judgement.
47 John uses martial imagery throughout Revelation, but some interpreters do not pick up that John's rhetoric is subversive.
48 This sword is not in the hand, as in normal warfare. Rather, this sword is out of the mouth, which makes all attempts to represent this artistically somewhat clumsy.
The only weapon in this war is words. Isaiah confirms this way of framing the conflict, as the expected Davidic ruler will "strike the earth with the rod of his mouth" and will vanquish the wicked "with the breath of his lips" (Isa 11:4 NRSV)
49 This conflict is of witness and testimony, the claims of Caesar versus the claims of Christ. The sword coming out of the mouth of the Son of Man is the theological equivalent of Jesus' penetrating question to his disciples in Mark 8:29 - "Who do you say that I am" - now addressed to believers in late first-century Asia Minor. John's sword has two characteristics. Being sharp, the sword cuts through anything, including Roman imperial propaganda, as in Virgil's almost euphoric celebration of the world Augustus created as savior and peacemaker.
50 Being two-edged, the sword cuts two ways, negatively as judgement, but positively as salvation.
51 John's uses here echoes that in Hebrews, "For the Word of God is living and active and sharper than any two-edged sword, and piercing even as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart" (Hebrews 4:12).
A two-edged sword cuts "both ways." The Word of God which is sent to bring salvation brings judgement if rejected. Commenting on John 5:24-27 Craig R. Koester says:
In positive terms, Jesus promised that anyone "who hears my word and believes him who sent me has eternal life; he does not come into judgement, but has passed from death to life" (5:24)...In negative terms, those who do not believe in him remain under divine judgement.
In Hebrews the two-edges refer to the faith of the believer (cf. Hebrews 4:1-3). The sword pierces to the division of the soul and is discerning the thoughts and intentions of the heart: it knows the truth of one's profession of faith. Chapter 4 of Hebrews addresses hearing His voice and hardening heart. Both of these may go "either way". It is possible to ignore His voice and harden the heart.
The macharia is active. It can reveal if one has heard or not; more importantly it is not symbolic of final judgment as the rhomphaia because it is living, it can change the hardened heart.
A Two-Edged Sword/Word Picture
The two-edged sword which is symbolic of the Word of God, calls a reader to both Greek and Hebrew texts. In Hebrew, פֶּה is the word for both mouth and edge. דָּבָר is word but these same consonants can be pronounced דֶּבֶר, which is "pestilence" or "plague." The imagery of a two-edged sword coming from the mouth creates an interesting picture:
The mouth bringing the Word is the edge bringing pestilence, plague, or death.
3. Gerald L. Stevens, Revelation, The Past and Future of John's Apocalypse, Pickwick Publications, 2014, pp. 271-272
4. Craig R. Koester, Symbolism in the Fourth Gospel, Meaning, Mystery, Community, Fortress Press, 1995, p. 88
47. Anthony T. Hanson, The Wrath of the Lamb, SPCK, 1957, pp. 166-167
48. CF. David L. Barr, "The Lamb Who Looks Like a Dragon? Characterizing Jesus in John's Apocalypse" pp. 205-206 in The Reality of Apocalypse: Rhetoric and Politics in the Book of Revelation. Edited by David L. Barr, SBLSymS, Num. 39. Edited by Christopher R. Matthews, Society of Biblical Literature, 2006.
49. Isaiah's imagery in Isa 11:4 and John's imagery in Rev 1:16 echoes in the unusual description of the lawless one in 2 Thess 2:8, "whom the Lord Jesus will destroy with the breath of his mouth."
50. Ecl. 4. Ferguson pointed out the "almost 'messianic' aura that surrounded the expectations of the people in the Augustan age," Backgrounds of Early Christianity, Erdmans, 2003, p. 114. CF. Horace, Satires, Epistles, and Ars poetica, Translated by H. Rushton Fairclough, LCL 194, Harvard University Press, 1926, 2.1.15; Andrew Perriman, The Coming of the Son of Man: New Testament Eschatology for an Emerging Church, Paternoster, 2005, p. 163
51. Cf. Mitchell G. Reddish, Revelation, Smyth & Helwys, 2001, p. 41