...we should realize that there are three sources for our thoughts - God, the devil, and ourselves.
John Cassian... a Christian is quite certain to fall into the same sins which he condemns in another with merciless and inhuman severity, for 'a stern king will fall into misfortunes,' and 'one who stops his ears so as not to hear the weak, shall himself cry, and there shall be none to hear him' (Prov. 13:17; 21:13).
John Cassian...when we abandon visible riches... it is strange goods and not our own that we are leaving. And this is so even if we boast that we acquired them through our own efforts or that they were passed on to us as an inheritance. I say nothing is ours except what is in our hearts, what belongs to our souls, what cannot be taken away by anyone.
John CassianThe second request of the very pure soul is to see the coming of the Father's kingdom (cf. Mt. 6:10). What this means first of all is that each day Christ should reign among holy men. And this happens when the devil's power has been driven out of our hearts through the expulsion of sinful foulness and when God has begun to reign within us amid the good odors of virtue. With fornication vanquished, chastity rules; with anger overcome, peace is king; with pride under foot, humility is sovereign.
John Cassian...just as the edifice of all the virtues strives upward toward perfect prayer so will all these virtues be neither sturdy nor enduring unless they are drawn firmly together by the crown of prayer. This endless, unstirring calm of prayer... can neither be achieved nor consummated without these virtues. And likewise virtues are the prerequisite foundation of prayer and cannot be effected without it.
John Cassian