The author of Ephesians borrows from the Old Testament the extended metaphor of the armor of God and adapts it to proclaim that believers have God’s weaponry in their struggle against cosmic spiritual forces.
Old Testament prophets sometimes use the imagery of God or God’s elect wearing armor to fight on behalf of God’s justice (see, for example, Isaiah, son of Amoz, who prophesied in Jerusalem, is included among the prophets of the eighth century B.C.E. (along with Amos, Hosea, and Micah)--preachers who boldly proclaimed God's word of judgment against the economic, social, and religious disorders of their time. 11:5; 49:2; 59:17). In 1 Thessalonians 5:8, A Christian missionary who once persecuted the church adapts that imagery to encourage his readers to “put on the breastplate of faith and love, and for a helmet the hope of Salvation can mean saved from something (deliverance) or for something (redemption). Paul preached that salvation comes through the death of Christ on the cross which redeemed sinners from death and for a grace-filled life..” Ephesians extends the metaphor even further. Virtues such as truth, righteousness, and faith, as well as less specific things such as “whatever will make you ready to proclaim the gospel of peace,” are part of the ensemble. Even though a military metaphor is used, the passage is not a call to arms, but a call to withstand (see verse 13). Except for “the sword of the Spirit, which is the word of God” (verse 17b), all of the armor pieces mentioned are items meant to protect the wearer rather than harm an enemy.