And they went into Capernaum; and immediately on the sabbath he entered the synagogue and taught. And they were astonished at his teaching, for he taught them as one who had authority, and not as the scribes. And immediately there was in their synagogue a man with an unclean spirit; and he cried out, "What have you to do with us, Jesus of Nazareth? Have you come to destroy us? I know who you are, the Holy One of God." - Mark 1:21-24 (RSVCE)
At Capernaum, as at Nazareth, Jesus went to the synagogue on the Sabbath, day to listen to the reading of the Law. There happened to be present a possessed person who cried out in terror, and declared Jesus to be the Holy One of God.
In the present day, men laugh at the idea of possession, but Holy Scripture teaches its undoubted reality. The spirit of uncleanness is sometimes allowed to inhabit the human body, to control the actions, and speak through the mouths of men, often as the just punishment of long indulgence in sin. Pray God that the devil may never obtain any power or influence over you, as he does in greater or less degree over all who do not resist his evil suggestions.
The unclean spirit could not remain silent in the presence of the Son of God. It regarded Him with terror and dismay as its deadliest enemy, and at the same time its Lord. "What have we to do with Thee? Art Thou come to destroy us?" So evil ever shrinks before good. The followers of Jesus are powerful over evil spirits just in proportion as they share His holiness. If we were more like Him, the devil would fear us more, and evil would shrink away abashed in our presence.
The devils knew well the holiness of Jesus. They have a natural power to discern the true character of the hearts of men. They cannot read all our inmost thoughts, but they can form a very correct estimate of us; we cannot deceive them as we can deceive men. What a contempt they must have for me! How low must be their opinion of my virtue!
- taken from The Ministry of Jesus Christ: Short Meditations on the Public Life of Our Lord, by Father Richard Frederick Clarke, SJ