Stand therefore, having fastened on the belt of truth, and having put on the breastplate of righteousness, (ESV)
“The breastplate was usually a tough, sleeveless piece of leather or heavy material with animal horn or hoof pieces sewn on, covering the soldier’s full torso, protecting his heart and other vital organs.
Because righteousness, or holiness, is such a distinctive characteristic of God himself, it is not hard to understand why that is the Christian’s chief protection against Satan and his schemes. As believers faithfully live in obedience to and communion with Jesus Christ, his own righteousness produces in them the practical, daily righteousness that becomes their spiritual breastplate. Lack of holiness, on the other hand, leaves them vulnerable to the great enemy of their souls.”
- John MacArthur Study Bible notes.
A breastplate gives us protection. Satan will scheme against us. He will shoot his arrows. One of his main weapons of choice is accusations against us. Satan knows all about God’s perfection. He knows that God is completely holy and righteous in all his ways. He can’t be anything but perfectly holy and righteous. What is Satan accusing us of? Our sin! Can we withstand the accusation? What kind of righteousness do we have to protect ourselves from these accusations?
There is a righteousness that will protect us from the true accusations of the enemy. It is not a righteousness that we are born with. No, the righteousness that we are born with is not righteousness at all. It falls short of God’s standard. God accomplished something amazing for us. He sent his son to die for the payment of our sins so that we could be given a free gift of his righteousness. It is a perfect righteousness, and it comes from a holy, perfect God. It comes by faith.
The breastplate of righteousness is your great defense. But, be warned. The enemy will want you to rely on the breastplate of your own righteousness. He will want you to reject God's perfect righteousness that is given to you. And the breastplate of your own righteousness is like a cardboard shield against fiery arrows. You will be destroyed. But, if you will reject the notion of your own righteousness, and receive by faith the gift of God's righteousness, you can respond to the enemy himself with boldness. Listen to how the great Martin Luther would respond to the enemy:
“So when the devil throws your sins in your face and declares that you deserve death and hell, tell him this: "I admit that I deserve death and hell, what of it? For I know One who suffered and made satisfaction on my behalf. His name is Jesus Christ, Son of God, and where He is there I shall be also!”
― Martin Luther