“…and take the helmet of salvation, and the sword of the Spirit, which is the word of God.” (Ephesians 6:17 (ESV)
It should be noted that of all the previously mentioned armaments the Christian has at their disposal, they are all defensive weapons by design. The only offensive weapon the believer in Christ possesses is the Word of God. What the Apostle Paul probably had in mind was the Roman sword. It was short and designed for hand to hand combat.
When the devil tempted Jesus (Matthew 4:1-11; Luke 4:1-13), the Lord repeatedly used the Word of God in His battle. Several prophecies teach that the words of the Messiah will be like a sharp sword (Isaiah 49:1-2; Revelation 1:16; 2:12-16; 19:15). All followers of Christ have this weapon at their disposal.
Dr. R. C. Sproul comments, “Ancient Roman soldiers carried different weapons, and the sword Paul likely has in view is the short-handled sword used in offensive combat against the enemies of the Caesar’s legions. In the Christian life, this sword is the Word of God (Eph. 6:17). Commentators believe Isaiah 11:4 is an important background text here. The Messiah strikes “the earth with the rod of his mouth” in that prophecy, so Paul may be emphasizing the preached Word of God as our offensive weapon against Satan. This makes good sense, for as the Word is preached, sinners are rescued from the Devil’s grip and believers see the sins for which they need to repent.”
Hebrews 4:12 says, “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.”
2 Corinthians 10:3-5 says, “3 For though we walk in the flesh, we are not waging war according to the flesh. 4 For the weapons of our warfare are not of the flesh but have divine power to destroy strongholds. 5 We destroy arguments and every lofty opinion raised against the knowledge of God, and take every thought captive to obey Christ.”
Dr. John MacArthur writes, “As the sword was the soldier’s only weapon, so God’s word is the only needed weapon, infinitely more powerful than any of Satan’s. The Greek term refers to a small weapon (6–18 inches long). It was used both defensively to fend off Satan’s attacks, and offensively to help destroy the enemy’s strategies. It is the truth of Scripture.”
Soli deo Gloria!