“And the sword of the Spirit, which is the word of God" Ephesians 6:17.
Here we have the sixth and last piece in the Christian's armor brought to our hand-- the sword of the Spirit. Throughout the ages the sword has been a most necessary part of the soldiers equipment and has been used more than any other weapon. A pilot without his chart, a student without his book, a soldier without his sword-- all are ridiculous. But above these, it is absurd to think of being a Christian without knowledge of God's Word and some skill to use this weapon.
The usual name in Scripture for war is "the sword." "I will call for a sword upon all the inhabitants of the earth" Jeremiah 25:29 ; that is, "I will send war." Now such a weapon is the Word of God in the Christian's hand. By the edge of this sword his enemies fall and all his great exploits are done: "They overcame him by the blood of the Lamb, and by the word of their testimony" Revelation 12:11. But before we enter into a detailed discussion of the sword of the Spirit, let us notice the kind of arms here presented for the Christian's use and the place and order in which it stands.
This weapon is both defensive and offensive. The rest of the apostles' armor pieces are defensive arms-- girdle, breastplate, shield, and helmet. But the sword both defends the Christian and wounds his enemy.
No matter how glorious the Christian's other pieces of armor, he would easily be disarmed without a sword in his hand. And surely the believer would be stripped of all his graces if he did not have this sword to defend them and himself too against Satan's fury. "Unless your law had been my delight, I should then have perished in mine affliction "Psalm 119:92.
This is like God's flaming sword, which kept Adam out of paradise. The saint is often compared to Christ's garden and orchard; and with the sword of the Word he keeps his orchard from being robbed of God's sweet comforts and graces by Satan's constant invasions.”
Quoted material from, ”The Christian in Complete Armour Daily Readings in Spiritual Warfare” by Gurnall and James S Bell. http://www.moodypublishers.com/pub_productDetail.aspx?id=41823&pid=53617