The second armor given to us is the breastplate of righteousness. The breastplate is meant to protect the most imprtant organ of the body – our heart. The Scripture tells us to watch over our hearts for out of the heart flows life.
Prov. 4:23 Above all else, guard your heart, for everything you do flows from it.
The heart is the seat of our emotions. You get the heart, you get everything.
1Th. 5:8 But since we belong to the day, let us be sober, putting on faith and love as a breastplate, and the hope of salvation as a helmet.
What is the basis of our righteousness? It is not our good works but the work Christ did at the cross thus we dont need to boast about our good works but rely on the grace God has given us to do good works. In short, we are made righteous because of what Christ. In reminds us again that Christ has fought the battle for us and all we need to do is yield to Him so that we can experience victory
2Cor. 5:21 God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.
Phil. 3:9 and be found in him, not having a righteousness of my own that comes from the law, but that which is through faith ina Christ—the righteousness that comes from God on the basis of faith.