St. Mark 1:23-28.— And there was in their synagogue a man with an unclean spirit; and he cried out, saying, Let us alone; what have we to do with Thee, Thou Jesus of Nazareth? Art Thou come to destroy us? I know Thee Who Thou art, the Holy One of God. And Jesus rebuked him, saying, Hold thy peace, and come out of him. And when the unclean spirit had torn him, and cried with a loud voice, he came out of him. And they were all amazed, insomuch that they questioned among themselves, saying, What thing is this? What new teaching is this? For with authority commandeth He even the unclean spirits, and they do obey Him. And immediately His fame spread abroad throughout all the region round about Galilee.
The evil spirits are called unclean because they wickedly take pleasure in every kind of shameful deed. Moreover, the demon considers his departure from the man to be his own destruction; for the demons are without pity and believe that they suffer ill if they are not permitted to do evil to men. Also, because they love the flesh and are accustomed to feeding upon carnal vapors, they are starved when they do not dwell within a body. This is why the Lord says that the demons come out of a man by fasting. The foul demon did not say, “Thou art holy,” for there were many prophets who were also holy. Instead he said, “The Holy One,” with the article; that is, He Who alone and by definition is Holy. But Christ shut his mouth in order to teach” us that even if the demons speak the truth we must curb them.* […] A scholion in the Greek text adds: “The Lord curbed the demon. For Truth had no need of recommendation by the evil spirits, nor to be praised by the testimony of Its adversaries. At the same time He hands down to us the salvific teaching that we should never believe the demons, even if they assert that they are speaking the truth. Since the demon spoke in a sober and composed manner, and all those present supposed that the words came from the heart of the man, and not from the demon, the Lord permitted the demon to throw the man down so that it would be clear that the words were demonic, and not spoken by the man. The demon ‘came out of him’ without harming him. For when the Lord cast him out, the demon did no harm; but the Lord permitted him to throw the man down for the sake of those present, but allowed no harm to be done, so that the power of Him Who commanded might be revealed.” ] The demon throws the man down and rends him so that those who witnessed this would see from what great evil the man had been delivered, and would believe in Christ because of the miracle.
—The Explanation by St. Theophylactos, Arcbishop of Ochrid & Bulgaria