From: Mark 1:21-28
Jesus in the Synagogue of Capernaum
 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."  But Jesus rebuked him saying, "Be silent, and come out of him!"  And the unclean spirit, convulsing him and crying out with a loud voice, came out of him.  And they were all amazed, so that they questioned among themselves, saying, "What is this? A new teaching! With authority He commands even the unclean spirits, and they obey Him."  And at once His fame spread everywhere throughout all the surrounding region of Galilee.
21. "Synagogue" means meeting, assembly, community. It was--and is--used by the Jews to describe the place where they met to hear the Scriptures read, and to pray. Synagogues seem to have originated in the social gatherings of the Jews during their exile in Babylon, but this phenomenon did not spread until much later. In our Lord's time there were synagogues, in Palestine, in every city and town of any importance; and, outside Palestine, wherever the Jewish community was large enough. The synagogue consisted mainly of a rectangular room built in such a way that those attending were facing Jerusalem when seated. There was a rostrum or pulpit from which Sacred Scripture was read and explained.
22. Here we can see how Jesus showed His authority to teach. Even when He took Scripture as His basis--as in the Sermon on the Mount--He was different from other teachers, for He spoke in His own name: "But I say to you" (Matthew 7:28-29). Our Lord speaks about the mysteries of God, and about human relationships; He teaches in a simple and authoritative way because He speaks of what He knows and testifies to what He has seen (John 3:11). The scribes also taught the people, St. Bede comments, about what is written in Moses and the prophets; but Jesus preached to them as God and Lord of Moses himself (St. Bede, "In Marci Evangelium Expositio"). Moreover, first He does and then He preaches (Acts 1:1)--not like the scribes who teach and do not do (Matthew 23:1-5).
23-26. The Gospels give us many accounts of miraculous cures, among the most outstanding of which are those of people possessed by the devil. Victory over the unclean spirit, as the devil is usually described, is a clear sign that God's salvation has come: by overcoming the Evil One, Jesus shows that He is the Messiah, the Savior, more powerful than the demons: "Now is the judgment of this world, now shall the ruler of this world be cast out" (John 12:31). Throughout the Gospel we see many accounts of this continuous and successful struggle of our Lord against the devil.
As time goes on the devil's opposition to Jesus becomes ever clearer; in the wilderness it is hidden and subtle; it is noticeable and violent in the case of possessed people; and radical and total during the Passion, the devil's "hour and the power of darkness" (Luke 22:53). And Jesus' victory also becomes ever clearer, until He triumphs completely by rising from the dead.
The devil is called unclean, St. John Chrysostom says, because of his impiety and withdrawal from God. In some ways he does recognize Christ's holiness, but this knowledge is not accompanied by charity. In addition to the historical fact of this cure, we can also see, in this possessed man, those sinners who must be converted to God and freed from the slavery to sin and the devil. They may have to struggle for a long time but victory will come: the Evil One is powerless against Christ (cf. note on Matthew 12:22-24).
27. The same authority that Jesus showed in His teaching (1:22) is now to be seen in His actions. His will is His command: He has no need of long prayers or incantations. Jesus' words and actions already have a divine power which provokes wonder and fear in those who hear and see Him.
Jesus continues to impress people in this way (Mark 2:12; 5:20-42; 7:37; 15:39; Luke 19:48; John 7:46). Jesus of Nazareth is the long-awaited Savior. He knows this Himself and He lets it be known by His actions and by His words; according to the gospel accounts (Mark 1:38-39; 2:10-11; 4:39) there is complete continuity and consistency between what He says and He does. As Vatican II teaches ("Dei Verbum", 2) Revelation is realized by deeds and words intimately connected with each other: the words proclaim the deeds and clarify the mystery contained in them; the deeds confirm the teaching. In this way Jesus progressively reveals the mystery of His Person: first the people sense His exceptional authority; later on, the Apostles, enlightened by God's grace, recognize the deepest source of this authority: "You are the Christ, the Son of the living God" (Matthew 16:16).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.