Elder Joseph the Hesychast. "Monastic Wisdom".
So, my priest, that lady you wrote about is a holy soul. But see to it that you explain to her the things I shall write here, so that she will be careful. For the enemy does not sleep; he hates man, and contrives everything to deceive him. Since she suffers such a martyrdom from her husband, God comforts her with those consolations and various visions. But she should not consider such things to be the main power of “the prayer,” because the evil one intervenes and quickly changes things.
The main power of the prayer and the entire appetitive power of the soul lies in the cleansing of the heart by means of noetic prayer. What does the Lord say? “Blessed are the pure in heart, for they shall see God.” He does not say, “Blessed are those who see visions and revelations.” So one should not rejoice in these things, even if they are from God. But one should rejoice when one sees that the nous has found the heart and remains inside it. Then the entire body is at peace, the soul is calmed, the heart leaps, the nous illuminates its powers, and tears run like a stream. The evil one is able to transform everything, but these things that we are talking about now, he cannot imitate. Nevertheless, when she sees something, she should not tell anyone about it, except her elder and spiritual father—no one else.
These things are happening now because she is suffering and has great simplicity and fear of God. But these things do not last until the end; the evil one changes them when he finds a way. Later, they lead to delusion. Therefore, much caution and humility are needed. She must think of herself as a worm of the earth, and only accept as true whatever her spiritual father tells her. Because if she starts accepting them, in a little while her thoughts will become sick, and she will end up accepting all demonic and silly things as true and sent from God.
What happens after that? A person becomes the mock of the demons. They fool him with writings and visions, with dreams and revelations, with symbols and numbers, with oracles and a heap of superstitions. May God protect her from this kind of change. Therefore, my priest, see to it that your Reverence always humbles her, lest her thoughts change and she becomes proud.