Gibbs, Jeffrey A. “Matthew 8:28-34: The Gadarene Exorcisms." Matthew 1:1-11:1. St. Louis: Concordia Publishing House, 2006, pp. 447-453.
Gibbs observes that the location Matthew refers to in 8:28 is unclear. There are numerous variants in spelling in the manuscript tradition, which leaves us uncertain of the identity of the location of these exorcisms (Gibbs 2006, 447). The herd of pigs present strongly suggests a predominantly Gentile territory. The deportation of the demons into the pigs and the pigs' death both released the demons and drew the attention of the herders (Gibbs 2006, 448).
In the Sermon on the Mount Jesus showed his authority b teaching. Here, in Matthew 8-9, he is showing authority by performing miracles. Gibbs sees this passage as a particularly vivid account which points to both the terror of the demonic and the authority of God (Gibbs 2006, 449).
The setting, according to Gibbs, would even speak of despair and defilement when considered by Gentiles, as the men were outcasts and living among the tombs (Gibbs 2006, 450). The demons are able to identify Jesus, but are surprised to see him before the time of thier final destruction. Gibbs notes that though they beg Jesus for answers, he doesn't answer their questions until he sends them into the herd of pigs (Gibbs 2006, 451). Jesus is the one who shows authority throughout this passage.
Gibbs observes that the demons remained subject to Jesus' authority once they were in the pigs. They had to destroy something so as to be set free. The drowning of the pigs accomplished this and also set the stage for a conversation between Jesus and the townspeople (Gibbs 2006, 452). Though the people recognize Jesus' authority they do not act in faith, but rather in fear.
Gibbs observes that demon possession accounts are rare in the Bible outside of the Gospels. He considers it likely that there are still cases of possession, but that they are increasingly rare because Satan is a defeated enemy (Gibbs 2006, 453). Christians, as people indwelt by the Holy Spirit, may be attacked by demons, but should take hope and confidence from the fact that Jesus in us is greater than any opposition.