having put on the breastplate of righteousness,
The overlapping metal strips of the Roman breastplate made it virtually impenetrable. It covered both the front and back of the soldier and had additions for each arm. Though it provided incredible protection, it was heavy and awkward to wear and required a great deal of training to be worn effectively.
It often chafed a soldier’s skin, creating sores that could be incapacitating. To keep this from happening, a tunic was worn under the armor, but a special piece was needed to protect the neck from chafing. This piece of bright red fabric was called the focale. Although it protected the skin from chafing, it created a vivid target for enemy archers who could kill the Roman soldier with one arrow strategically aimed where the focale protruded from the breastplate at the base of the throat. Some believe this is where the term “focal point” is derived from.
Paul says the breastplate that will protect the Ephesians is righteousness. Here, he is referring to practical righteousness, the right choices a believer must make every day to stand against temptation and live a life of godliness. That kind of righteousness, however, can be heavy and uncomfortable, sometimes even awkward. Each compromise made to eliminate the chafing could create a focale: the perfect target for the enemy.