At the end of the Sermon on the Mount Matthew talks about people being astonished because Jesus spoke as one who had authority (Matthew 7:28-29 And when Jesus finished these sayings the crowds were astonished at his teaching for he was teaching them as one who had authority). In the follow 2 chapters (Matthew 8-9) he goes on to give us 14 ways Jesus proved that authority by His actions.  In Matthew 8-9, Matthew is trying to get us to see that authority because it is not only the authority of a King, but also the authority of our great God.