Ephesians 6:14-17 New International Version
“Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, and with your feet fitted with the readiness that comes from the gospel of peace. In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. Take the helmet of salvation and the sword of the Spirit, which is the word of God.”
The physical breastplate defends all the vital organs that are contained in the thorax. In the same way the breastplate of righteousness defends everything on which the man’s spiritual existence depends. 
Okay, so if no one is righteous on his own, then how do we become righteous so we can have this breastplate to protect ourselves against the fiery arrows of the enemy? We cannot earn it. We cannot buy it. It is ours when we receive Christ into our lives. His righteousness becomes our righteousness. We are now members of God’s family and therefore are seen by Almighty God as righteous in His sight.
We must wear it to ward off the slanderous accusations that Satan will hit us with. We are no match for him on our own, but with the power of God at our disposal we are unbeatable. One word in Jesus name and the devil and all his demons must flee. Take seriously your charge as a believer in Christ. Seek to live humbly and obediently to the word of God and strive to be more like Jesus each day. Bless someone today in word or deed. Until next time, walk with the King and be a blessing!
 Taken from Christian website http://www.gladiatorsforgod.com/armour_02_breastplate.htm