Gird Your sword on Your thigh, O Mighty One, in Your splendor and majesty!
The power of the Word is shown in this, that Christ fights in us with His armament, "with the breastplate of faith and the sword of the Word" (Ephesians 6:16-17). So we strike the enemy on all sides, first by laying bare his deceit and lies in the heretics, then by snatching up and defending our men so that they may persevere in holy faith and life. . .. You see here what kind of king we have. After He has taught us and poured out His promises on us, and by His Word has transferred us into His kingdom (Colossians 1:13), Satan is immediately there and crucifies us. For "all who wish to live a godly life in Christ must bear persecution" (2 Timothy 3:12); similarly, "through many tribulations we must enter the kingdom of God" (Acts 14:22). But our King will not forsake us. He is present and fights in us against the power of tyrants and against the lies of the devil. Indeed He renders us invincible against the lying teachers and secure against the power of tyrants.
From Lectures on Psalm 45 (Luther's Works 12:216)