Here in Ephesians Paul tells us to put on the full armor of God that we can withstand the devil. He says to gird ourselves with truth, to put on the breastplate of righteousness, shod our feet with the Gospel and have the shield of faith. We need all this as preparation, we can’t go into battle with the devil not knowing God’s word. Having it hidden in our hearts is what will protect us. Being able to recall it when we need it can be what saves us from a fiery dart, just like Jesus did