Guard thyself then, O man; thou hast the signs of Antichrist; and remember them not only thyself, but impart them also freely to all. If thou hast a child according to the flesh, admonish him of this now; if thou hast begotten one through catechizing, put him also on his guard, lest he receive the false one as the True. For the mystery of iniquity doth already work. I fear these wars of the nations; I fear the schisms of the Churches; I fear the mutual hatred of the brethren. But enough on this subject; only God forbid that it should be fulfilled in our days; nevertheless, let us be on our guard. And thus much concerning Antichrist.
But let thine apparel be plain, not for adornment, but for necessary conversing: not to minister to thy vanity, but to keep thee warm in winter, and to hide the unseemliness of the body: lest under the pretence of hiding the unseemliness, thou fall under another kind of unseemliness by thy extravagant dress.
We believe that the divine presence is everywhere and that 'the eyes of the Lord are looking on the good and the evil in every place.' But we should believe this especially without any doubt when we are assisting at the Work of God. To that end let us be mindful always of the Prophet's words, 'Serve the Lord in fear' and again, 'Sing praises wisely' and 'In the sight of the Angels I will sing praise to Thee.' Let us therefore consider how we ought to conduct ourselves in the sight of the Godhead and of His Angels, and let us take part in the psalmody in such a way that our mind may be in harmony with our voice.
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.
The view we take of our Savior's dispensation is the view of the holy fathers who preceded us. By reading their works we equip our own mind to follow them and to introduce no innovation into Orthodoxy.