Let us, therefore, take courage and strip ourselves for the contests. Christ has put on us armor that is more glittering than any gold, stronger than any steel, hotter and more violent than any fire, and lighter than any breath of air. The nature of this armor does not burden and bend our knees, but it gives wings to our limbs and lifts them up. If you wish to take flight to heaven, this armor is no hindrance. It is a new kind of armor, since it is a new kind of combat.
Although I am human, I must aim my blows at demons; although clad in flesh, my struggle is with incorporeal powers. On this account God has made my breastplate not from metal but from justice; God has prepared for me a shield which is made not of bronze but of faith. I have, too, a sharp sword, the word of the Spirit.
John Chrysotom, Fourth Century