Paul explained to the Ephesians (and to us) to always be prepared to fight off the devil by using the whole armor of God. In Ephesians 6:11 he details that armor. Our weapon of choice to go along with that armor is a sword. The sword of the Spirit, which is the word of God (6:17). That sword will only do us good if we use it. Not only when we are in need, but we must read and study from it often to be prepared for whatever Satan will throw at us.