Paul continues to tell us what is the next piece of Spiritual weaponry.
Righteousness is a weapon, it is our breastplate.
We know that it is a weapon because Paul calls it a weapon in the six chapter of Ephesians. The breastplate was the most beautiful, shiniest, most glamorous peace of weaponry that the Roman Soldier possessed. When you walked up to a Roman soldier the first thing that you would notice was his breastplate. The Holy Spirit tells us that our breastplate is to protect us. The devil wants to play games with your minds by telling us that we are not righteous.