Although science believes that demons do not exist, Jesus had no such problem.  When evil spirits spoke through the commandeered mouths of their victims, Jesus heard them, spoke back to them and they obeyed His orders.  This narrative immediately follows Jesus' teaching in the synagogue in Capernaum, when all the people were amazed by the compelling authority with which He taught (Mark 1:21-22).  But they did not know why He sounded so completely 'at one' with God's Word.

One man was present who was being controlled by a demon.  He shouted out to Jesus, on behalf of his captor in great fear, knowing that Jesus could destroy the devil, his agents and people who accepted evil (Revelation 20:10).  With startling clarity the demonised man announced Jesus as the 'Holy One of God'.  That was a Messianic title, probably from Psalm 16:10, referring to Christ's death-without-decay and His resurrection.  Even though the people might have wondered who Jesus was, the angels of Satan were fully aware that His task was to destroy their kingdom.  Interestingly, the demonic 'confession of faith' was insightful and fearful, but was certainly not mixed with repentance.  It is therefore a sobering possibility that someone may know about Jesus, and even shout out the facts of the gospel, but not be 'on side' with the Lord (Matthew 7:21-23).  James 2:19 says, "You believe that there is one God.  Good!  Even the demons believe that – and shudder."

The demon was expelled, and the man was left shaken and alone without his evil companion.  This exorcism was no illusion; the crowd recognised that if Jesus had power over demons then His words must carry awesome weight.  Which they do.  The story after that changes its focus.  We do not know if the man did repent and welcome Jesus.  But if he did not welcome Jesus, he was at serious risk of an even greater invasion of evil (Luke 11:24-26).  Mark identifies 10 exorcisms to show Jesus' power over the devil and his demons.  This is intentional.  Jesus did not just come to teach, set a good example and demonstrate God's love.  He came to overthrow the power of Satan and release people who had been taken captive by him (Hebrews 2:14-15) – saving them from hell and giving them eternal life (John 10:28).  

Christ's authority is still effective in rescuing people from evil.  2 Peter 2:20 is a potent reminder not to slip back into the devil's clutches, "If they have escaped the corruption of the world by knowing our Lord and Saviour Jesus Christ and are again entangled in it and are overcome, they are worse off at the end than they were at the beginning."  As Ephesians 6:12 says, "… our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms."  Let us not be naïve: we are in a spiritual battle, but Jesus has the authority to oust the enemy.  So, "Submit yourselves, then, to God. Resist the devil, and he will flee from you. Come near to God and he will come near to you." (James 4:7-8).