(I figured it had been so long, I'd go ahead and do tha whole chapter today).
I'm also not going to cut and paste the whole chapter. Go here
and read it.
Jesus starts off the chapter by showing His sovereignty over demons by casting them out. The demoniac has been afflicted for some time, and has either left or been run out of the city. He lives among the tombs -- caves, in other words. The Bible also makes sure we know just how strong this guy was -- his shackles and chains had been broken many times before. Nobody wanted to mess with the guy.
The demons know exactly who Jesus is. Verse 7 -- "What have you to do with me, Jesus, Son of the Most High God? I adjure you by God, do not torment me." The demons are begging for their survival -- they are afraid that Christ has come to finally condemn Satan and his followers to the pit or all eternity. Christ knows that that time has not yet come. But He delivers the man from the demons.
I don't know why He sent the demons into the swine. I DO know that this caused the people who owned the swine to be VERY upset at Him. Maybe these people were Jews who weren't supposed to be tending pigs (unclean animals), and Christ was rebuking their rebellion. In any case, when word got around about what had happened, people came to check things out. I think their reaction is interesting. "... they were afraid. ... And they began to beg Jesus to depart from their region." They didn't know who this guy was, but they knew they didn't want Him around. He was causing problems. He was making them re-evaluate the way things were.
That's what Jesus does when He enters our lives. We have to re-evaluate things. Our priorities change. Our goals change. Even our speach may change. Our attitudes and outlook change. Christ challenges us to think the way He thinks. And many people don't like that. They are afraid of changing the way they think. They don't want to view the world the way Christ does -- as sinful people in need of a Savior. They don't want to feel what He felt as He looked over Jerusalem. They want to continue to pursue their own goals and dreams, and not subordinate them to Christ's will. And they know that Christ requires them to do exactly that.
Unfortunately, many Christians don't recognize that. We pray the prayer, walk the aisle. We get dunked. We sign a membership card. We go to Sunday School. And Christ never makes an impact on our lives at all. We are living with the form of Godliness, but we deny it's power. Power over our world, but also it's power over us. Our challenge is to live each day, more and more conformed to the image of Christ, and to see everything the way He sees it.