5 We discoursed to you yesterday about the power which is in prayer. I pointed out how the devil then lies in wait, deceiver that he is. For since he sees very great gain accruing to us from prayer, then most he assails us, in order that he may disable us from our defence; that he may send us off home empty-handed. And just as before magistrates, when the officers of the court who are about the person of the magistrate have a hostile feeling toward those who come before him, they by their staves drive them away to a distance, preventing their coming near and resorting to lamentation and so obtaining compassion; so also the devil, when he has seen us coming to the judge, drives us away to a distance, not by any staff, but through our own slackness.
For he knows, he knows clearly, that if they have come to him in a sober spirit, and have told the sins committed, and have mourned with their soul fervent, they will depart having received full forgiveness; for God loves mankind; and on this account he is beforehand with them, and debars them from access, in order that they may obtain no one of the things which they need. But the soldiers of magistrates with violence scare away those who are coming to them; but he with no compulsion, but by deceiving us, and throwing us into security.
On this account we are not deserving even of allowance, since we voluntarily deprive ourselves of the good things. Prayer with earnestness is a light of the understanding and soul— a light unquenchable and perpetual. On this account he throws into our minds countless rubbish-heaps of imaginations; and things which we never had imagined, these collecting together at the very moment of prayer he pours down upon our souls. And just as winds often rushing from an opposite quarter by a violent gust extinguish a lamp's flame as it is being lighted, so also the devil, when he has seen the flame of our prayer being kindled, blowing it on every side with the blasts of countless thoughts, does not desist before and until he has quenched the light.
But the very thing which they who are kindling those lamps do, this let us also do. And what do they do? When they see a violent wind coming, by laying their finger upon the opening of the lamp they bar the entrance against the wind. For so long as he assails from without we shall be able to stand against him; but when we have opened to him the doors of the mind, and have received the enemy inside; after that we are no longer able to withstand even a little; but, having on all sides completely extinguished the memory, just as a smoking lamp, he allows our mouth to utter empty words.
But just as they put their finger upon the opening of the lamp, so let us lay consideration upon our mind: let us close off from the wicked spirit the entrance, in order that he may not quench our light of prayer. Remember both those illustrations, both that of the soldiers and the magistrate, and that respecting the lamp. For with this purpose we adduce to you these illustrations; with which we are conversant, in which we live, in order that, after we have departed hence and have returned home, we may from things of familiar occurrence receive a reminder of what has been said.
Source: Homily Against Publishing the Errors of the Brethren (New Advent)