Breastplate of righteousness

The breastplate is a needed part of any armour set, it's the major defence of the body and is second in defensive capabilities next to the shield, in fact I'd call it the second line of defense also the colours of your tabard which can accompany a breastplate can identify which army you are fighting for.

I would say all this relates to righteousness, which is to be right with God. Firstly we are defended through our righteousness from the attacks of Satan. We are told in the same passage as the breastplate of righteousness that the shield of faith will extinguish the flaming arrows of the enemy, well I believe that's true and whilst the shield of faith can do this, our righteousness can stop those extinguished arrows completely removing the pain they will bring us from coming to us. Yet as like a breastplate our righteousness should be tended to after each battle in so far as to keep ourselves right with God we should confess our sins to Him after every battle we have in this life. 

Also we are identified as a member of the army of Christ through our righteousness and salvation in Jesus Christ. As members of an army we don't fight alone, which is good since a breastplate doesn't have a back and so is, in some ways, designed for fighting as an army facing the opponent down. We should not fear Satan and his attacks but rather face him and challenge him so that he shall flee.