+Bishop Christodoulos : About Dreams
Demons often transform themselves into angels of light and take the form of martyrs, and make it appear to us during sleep that we are in communication with them. Then, when we wake up, they plunge us into unholy joy and conceit. But you can detect their deceit by this very fact. For angels reveal torments, judgments and separations; and when we wake up we find that we are trembling and sad. As soon as we begin to believe the demons in dreams, then they make sport of us when we are awake too. He who believes in dreams is completely inexperienced. But he who distrusts all dreams is a wise man. Only believe dreams that warn you of torments and judgments. But if despair afflicts you, then such dreams are also from demons.
---St. John Climacus, The Ladder of Divine Ascent
Inasmuch as we know the true sign and image of the Cross, the devil does not dare to use it (for our deception); for on the Cross his power was destroyed, and by the Cross a fatal wound was given him. The Master Christ we cannot recognize by the flesh, which is why the devil tries to convince us by lying that it is He, so that having believed the deception as if it were truth, we might perish. And thus, when you see in a dream the image of the Cross, know that this dream is true and from God; but strive to receive an interpretation of its significance from the Saints, and do not believe your own idea. May the lord enlighten the thoughts of your mind, O brother, so that you might escape every deception of the enemy.
---Saints Barsanuphius and John: Guidance Toward Spiritual Life