A mind from which the thought of God has been carried away and which has thus become far removed from remembering Him, is also indifferent to sin with the outer senses. For such a mind can guide neither the hearing nor the tongue, since zest to work on itself has gone out of it.
Even a pious person is not immune to spiritual sickness if he does not have a wise guide -- either a living person or a spiritual writer. This sickness is called prelest, or spiritual delusion, imagining oneself to be near to God and to the realm of the divine and supernatural. Even zealous ascetics in monasteries are sometimes subject to this delusion, but of course, laymen who are zealous in external struggles (podvigi) undergo it much more frequently. Surpassing their acquaintances in struggles of prayer and fasting, they imagine that they are seers of divine visions, or at least of dreams inspired by grace. In every event of their lives, they see special intentional directions from God or their guardian angel. And then they start imagining that they are God's elect, and often try to foretell the future. The Holy Fathers armed themselves against nothing so fiercely as against this sickness -- prelest.
Go, sell all that belongs to you and give it to the poor and taking up the cross, deny yourself; in this way you will be able to pray without distraction.
Put aside bodily considerations when you stand in prayer, lest the bite of a flea, a gnat or a fly deprive you of the greatest gain afforded by prayer.
Pray before your body takes rest on your bed... If you are tempted, make the Sign (of the Cross) on your forehead reverently… for this is a known and tested weapon against the Devil.
Exercise patience out of love for your fellow man. Exercise patience in order to benefit your soul. For if you do not take your soul into consideration, you lose your patience.
Prayer demands that the mind should be pure of all thought and should admit nothing not belonging to prayer, even if it were good in itself. As if inspired by God the mind should withdraw from all things and hold its converse with Him alone.
Therefore with your whole soul you should acknowledge yourself as worthy of enduring more than you already endure; remember the words which Christ the Savior spoke concerning a good deed done to one's neighbor, words which should apply equally to every offensive word or deed against one's neighbor. Whatever you have done to your neighbor, He says, you have done to Me.