Putting on the Breastplate of Righteousness protects me from two avenues of Satanic attack.
On the one hand, we can get so focused on our authority in Christ, that we go to an unbiblical extreme that is really nothing more than sinful pride and arrogance. Putting on the breastplate of righteousness protects me from spiritual cockiness and arrogance, esteeming myself better than others, from self-confidence (rather than Christ-confidence), and from self-righteousness. Satan is extremely clever at slipping in this deception on believers. Some are especially susceptible to it. And often, when we have been drawn into it, we don’t recognize it in ourselves. We may think that we are being “spiritual” when we are really only being arrogant! If Satan can deceive us here, we are greatly hindered in our effectiveness for the Lord.
The Breastplate of Righteousness also protects me from overwhelming vague feelings of condemnation and guilt (as a result of past sins). Without the breastplate of righteousness we can be paralyzed by feelings of unworthiness, worthlessness, hopelessness, and discouragement because of past failures. Without it we can feel so undeserving that we don’t expect anything from the Lord. Again, Satan knows that many Christians are susceptible to defeat at this point. It’s easy to make them feel so guilty and unworthy that they feel they can be of no use to the Lord. Great damage has been done by the enemy with this weapon on God’s people.