Ephesians 6:14 (KJV) says,
"...having put on the Breastplate of Righteousness ."
The Amplified Bible says,
"...having put on the breastplate of integrity and of moral rectitude and right standing with God."
That scripture is rooted in the righteousness that we already have in our standing before God through Jesus on the cross. When we put on the Breastplate of Righteousness we submit to the Lordship of Christ. We acknowledge that our righteousness "are like filthy rags" without His covering of righteousness (Isaiah 64:6).
The Breastplate of Righteousness does not refer to OUR righteousness or "holiness", but the right-standing with God because of our faith in Him and Jesus' work on the cross. It is nothing we have done or our works, but it is by the covering of Jesus Christ, His righteousness, His precious blood, over our hearts that are in tune and in unity with His spirit.
Look at the following scriptures:
Titus 3:5 "not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit;"
Philippians 3:9 "and be found in Him, not having my own righteousness, which is from the law, but that which is through faith in Christ, the righteousness which is from God by faith;"
II Corinthians 5:21 "For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him."
It is all about HIS righteousness that we put on or apply to our lives. But this does not mean that our heavenly Father is indifferent to our sin or regards it lightly. Rather, as a loving father corrects his child, so the Lord corrects us (Hebrews 12:5-11). At times His chastening may seem stern and unfair, but He is working to mold us into the likeness of Christ to let His righteousness shine forth in and from us, the Breastplate of Righteousness.
According to the significant amount of time that the Bible shows that Paul spent in prison, he had plenty of time to study the Roman soldier's armor and how it relates spiritually to individual lives and to the whole Body of Christ together.
The Roman soldier's breastplate was made of crafted or metal bands or iron, sometimes called "chain mail". It covered the body from the neck down to the thighs. It protected all of the vital organs, front and back (It was in two parts hooked or laced together), within the trunk of the body. Protecting the heart was the most important goal of the breastplate. Injury to the heart prevented the soldier from being able to fight or could even cause death.
In spiritual terms, why is it so important to protect the heart? A lot happens with and comes from the heart. We worship from the heart; We serve and love God with all of our heart. Proverbs 4:23 says,
"Keep thy heart with all diligence; for out of it are the issues of life."
The natural heart pumps life-giving blood throughout the body. Within your spirit, your heart causes the spirit of the Living God to flow within and bring life to your soul.
Your spiritual heart is a major target of Satan. He does not want you to do anything with all sincerity of your heart. He wants you to be apathetic about the things of God and about working for the Kingdom of God.
Satan also wants you to have an apathetic attitude toward sin, not thinking too much about how it is wrong. He wants us to have the "everybody else does that" attitude or "John does that, and he is suppose to be a Christian, so it must be okay." All deception! When that crosses your mind you have taken off or are about to take off your Breastplate of Righteousness. Pick it back up and put on your rightful protection against the enemies darts he is throwing at you.
He attacks the heart of your spirit by slowing down your spiritual heartbeat through being stressed and exhausted physically, mentally, and emotionally as a result of the overwhelming daily tasks in life and difficult circumstances.
Ever heard of the saying, "That broke my heart!" That simply means what was said or done to a person wounded their spirit. Hurt feelings can harm the heart of your spirit and the heart of your work for God. This not only involves individual attacks by Satan, but also involves attacks within the Body of Christ to bring disunity and causing the Church's heart for God to be distracted and causing the heart of their work to be hindered or stopped (spiritual heart attack).
Satan also tries to shoot arrows of accusations at the heart to cause deep wounds. He tries to inflict wounds of accusations. Revelation 12:10 says that Satan is called the "accuser of the brethren." There is a difference between conviction of the Holy Spirit and condemnation of Satan. When we sin, the Holy Spirit will convict us, deal with us about specific areas of sin, and draw us through repentance and forgiveness.
But Satan will counterfeit the conviction with accusations. The little voice in your mind that says, "You call yourself a Christian? Look at how you messed up this week! You can't really be a Christian (causing you to doubt your salvation)" is the voice of Satan or his demonic minions putting deceptive thoughts into your mind, the center of the battleground. When this happens, he is attacking your Breastplate of Righteousness.
The condemnation will come, but we must stand our ground, put on the Breastplate of Righteousness, and boldly say, "That is a lie, Satan! I'm complete in Christ. What I did wrong is in the past. If I confess my sins, God is faithful and just to forgive my sin and cleanse me of ALL unrighteousness! (I John 1:9)" We must be aware of Satan's strategy and gear up by putting on the spiritual armor including the Breastplate of Righteousness.