If you are looking for an in depth study of the armor of God I highly recommend this study by Priscilla Shirer. It is a seven session study so it may take some time but it really delves into scripture and how to fight spiritual warfare. Be warned however, if you start this study you will be challenged and maybe even attacked but you will definitely finish stronger than when you started. It goes in depth into each portion of the armor of God and its significance. I have never read a study where I learned so much that I could directly apply to my life. It is a powerful study book where you can journal your thoughts and prayers and really be challenged!