Excerpt from The Life of St. Antony:

So then we ought to fear God only, and despise the demons, and be in no fear of them. But the more they do these things the more let us intensify our discipline against them, for a good life and faith in God is a great weapon. At any rate they fear the fasting, the sleeplessness, the prayers, the meekness, the quietness, the contempt of money and vainglory, the humility, the love of the poor, the alms, the freedom from anger of the ascetics, and, chief of all, their piety towards Christ. Wherefore they do all things that they may not have any that trample on them, knowing the grace given to the faithful against them by the Saviour, when He says, "Behold I have given to you power to tread upon serpents and scorpions, and upon all the power of the enemy ."