What does Ephesians 6:14 mean?

The first two parts of God's armor are noted in this verse. Paul describes these parts of a Roman soldier's clothing in the order they would have been put on.

First, Paul mentions the "belt of truth." In that time, a belt was tied around the waist rather than buckled. It was therefore "fastened" as Paul notes. These were not thin, pretty strips of cloth, either. A soldier's belt was thick and sturdy, somewhat like what modern people would call a "weightlifter's belt." The rest of a soldier's armor connected to this belt. For the Christian, truth is to be securely connected to us, for our success. Truth, as Paul defined it, included the accurate information regarding God and the good news of Jesus (Ephesians 1:13; 4:15, 21, 25). From a logical standpoint, this is also a sensible statement. Truth "binds together" everything else we believe. Without unifying truth, we just have disjointed, disconnected pieces.

Second is the "breastplate of righteousness." This belt would hold the breastplate in place, as well as the scabbard to hold the sword (Ephesians 6:17). A Roman's breastplate would typically be made from bronze or chain mail and would cover the vital body parts (heart, lungs, stomach). Righteousness, or doing what is right, is essential to protecting the life of the believer through spiritual battle. Also, the breastplate is a primary means of identification: this is one of the clearer ways for soldiers to recognize each other in battle. Likewise, a Christian's behavior is meant to identify them to the world, and other believers, as a follower of Christ.