Joel 1:13-15; 2:1-2 / Luke 11:15-26
The presence of evil in person is often given a medical or psychological rationalisation in that it is an ailment that can be treated through medication and therapy.
As much as medication and therapy may be helpful, but from the gospels, it is clear that evil is caused by powerful demons that live in or occupy or possess a person who has given in willingly to these demons.
But when a person wants to be freed of these evil inhabitants, then we will understand why Jesus cast out demons.
Jesus came to break the power of evil over persons who want to be converted and to be freed from the power of evil.
But evil spirits or demons need embodiment, meaning to say that when an evil spirit is driven out of a person it will immediately look for another person to inhabit.
In the gospel, Jesus said when an evil spirit comes out of a person, it searches for another place of rest, i.e. another person to inhabit. Not finding one it goes back to the person it came out of and finds it ready and waiting. It even thinks of that person as its former "home". The spirit re-inhabits the person and brings seven other demons making the state of that person worse than before.
Hence for true conversion to happen, there also must be a continuing repentance.
Driving out the evil spirit is only the beginning. Jesus must be welcomed into the heart to make the heart His home and to keep the person protected from the infiltration of evil spirits who would want to occupy and possess the person again.
This is also a reminder for us to always consecrate our hearts to Jesus, to His Most Sacred Heart.
In our on-going conversion and repentance, we beseech the Lord Jesus to also make our hearts like His.