That there is a strong conflict to be waged against the devil, and that therefore we ought to stand bravely, that we may be able to conquer
In the Epistle of Paul to the Ephesians: “Our wrestle is not against flesh and blood, but against the powers and princes of this world, and of this darkness; against the spiritual things of wickedness in the heavenly places. Because of this, put on the whole armour of God, that you may be able to resist in the most evil day; that when you have accomplished all, you may stand, having your loins girt in the truth of the Gospel, putting on the breastplate of righteousness, and having your feet shod with the preparation of the Gospel of peace; in all things taking the shield of faith, in which you may extinguish all the fiery darts of the most wicked one; and take the helmet of salvation, and the sword of the Spirit, which is the word of God.”
Source: The Treatises of Cyprian (New Advent)