Three possible views why the demons begged Jesus to cast them into the herd of pigs:
Jesus’s defeat of the demons causes them to stoop to begging Jesus to cast them into the pigs, to at least postpone their torment for a little longer (Luke 8:31). Jesus then grants them this (Matthew 8:32).
Matthew 8:30–31 shows the demons’ desperation. Knowing that Jesus will never allow them to stop his ministry, and that he will inevitably drive them out, they seek permission to go into the herd of pigs that are grazing nearby. They are not necessarily looking for the closest and best place to flee, but rather of something further away. They deliberately choose something that would be anathema to Jesus as a Jew, but which is also a valuable asset to the people in the area— pigs—so that their flight would involve destruction to Jesus’ detriment.
The demons’ plea to be cast into the herd of swine should be seen in light of the fact that they knew that they no longer could possess the men they were in. The pigs were close by, and the demons hoped to possess them in an attempt to continue their work in trying to hinder Jesus’ work.
Interpretation 1:
In their attempt to try and ward off Jesus the complete powerlessness of the demon-possessed men in opposition to the Son of God is revealed. As such they resort to begging. They beg Jesus to cast them into the herd of pigs in order to at least postpone the eternal torment that awaits them in the abyss for a little while longer (Luke 8:31). Jesus then proceeds to grant them this (Matthew 8:32)1
Interpretation 2:
In Matthew 8:30–31 we find new proof of the agitated inconsistency on the part of evil spirits when devising tricks. Realistically, they know that the Son of God will never allow them to stop his ministry, and that he will inevitably drive them out. As such, they resort to seeking permission to go into the herd of pigs that are grazing nearby. The demons were here not necessarily looking for the closest and best place to flee, but rather of something further away. Their request, as such, purposely involved something that would be anathema to Jesus as a Jew, but which at the same time constituted a valuable asset to the people in the area: pigs. The idea behind this was that their flight would involve destruction to Jesus’ detriment.2
Interpretation 3:
The fact that the demons beg to be cast into the herd of swine needs to be understood in light of the fact that they realized that they no longer could possess the men they were in. The pigs were close by, and they had hoped to possess them in an attempt to continue their work in trying to hinder the work of Jesus3
30 Il y avait loin d'eux un grand troupeau de pourceaux qui paissaient.