The Christian's armour is both for defence and for attack

"So, dearly-beloved, let us who instructed in Divine learning come wittingly to the present contest and strife, hear the Apostle when he says, for our struggle is not against flesh and blood, but against principalities and powers, against the rulers of this dark world, against spiritual wickedness in heavenly things, and let us not forget that these our enemies feel it is against them all is done that we strive to do for our salvation, and that by the very fact of our seeking after some good thing we are challenging our foes. For this is an old-standing quarrel between us and them fostered by the devil's ill-will, so that they are tortured by our being justified, because they have fallen from those good things to which we, God helping us, are advancing. If, therefore, we are raised, they are prostrated: if we are strengthened, they are weakened. Our cures are their blows, because they are wounded by our wounds' cure. Stand, therefore, dearly-beloved, as the Apostle says, having the loins of your mind girt in truth, and your feet shod in the preparation of the gospel of peace, in all things taking the shield of faith in which you may be able to extinguish all the fiery darts of the evil one, and put on the helmet of salvation and the sword of the Spirit, which is the Word of God. See, dearly-beloved, with what mighty weapons, with what impregnable defences we are armed by our Leader, who is famous for His many triumphs, the unconquered Master of the Christian warfare. He has girt our loins with the belt of chastity, He has shod our feet with the bonds of peace: because the unbelted soldier is quickly vanquished by the suggester of immodesty, and he that is unshod is easily bitten by the serpent. He has given the shield of faith for the protection of our whole body; on our head has He set the helmet of salvation; our right hand has He furnished with a sword, that is with the word of Truth: that the spiritual warrior may not only be safe from wounds, but also may have strength to wound his assailant."

-- From a sermon by St Leo the Great