We read in Provervbs 4.23 "Keep your heart with all diligence, for out of it flows the wellspring of life." This is true in both the spiritual and physical sense. A direct wound to the heart on the battlefield could be fatal. That is why even modern warriors wear body armor that protects the area around the heart, a bullet-proof vest, and in ancient days a breastplate. As we wage spiritual war, and as we live in light of the real spiritual war going on around us, we must be sure that our heart, our lungs and other vitals here are protected.
But how do we protect our heart? In Ephesians 6.14 we read that we protect our heart with the breastplate of righteousness. And how do we put on the breastplate of righteousness? Through our faith in the finished work of Christ on the cross, his death that paid the punishment that we deserved, so that we could become the righteousness of God through faith in him.
In Romans 4.3ff we read "“Abraham believed God, and it was accounted to him for righteousness.” 4 Now to him who works, the reward is not counted as grace, but as something owed. 5 But to him who doesn’t work, but believes in him who justifies the ungodly, his faith is accounted for righteousness."
Later in the same chapter we read of Abraham: "22 Therefore it also was “credited to him for righteousness.” 23 Now it was not written that it was accounted to him for his sake alone, 24 but for our sake also, to whom it will be accounted, who believe in him who raised Jesus, our Lord, from the dead, 25 who was delivered up for our trespasses, and was raised for our justification.
5.1 Being therefore justified by faith, we have peace with God through our Lord Jesus Christ; 2 through whom we also have our access by faith into this grace in which we stand."
So we guard our heart, by holding on to this marvelous truth that we have been made righteous not because of our own ability to always do the right thing, or always choose the way of love, but because we believe in him who died for our sins and was raised for our justification. Our focus for our righteousness is not our on ability and track record to be perfectly righteous, our focus is the work of Christ on our behalf.
This is our breastplate of righteousness. Amen. Praise the Lord!