The Church Militant is under constant attack by the world, our flesh and the evil one. How do we contend against such powers? They are too strong for us, but there is One who has and continues to fight in our place on our behalf.
Paul is talking about military-level allegiance here, the strongest kind of allegiance sworn to a king. Yet, this loyalty is set in contrast to the tasks of the Roman solider because the task of Christ’s legionaries is to herald the good news: their King, Jesus, has won and it is He who is the world’s rightful king.