One pastor with his associates tried to cast out a demon that possessed a man. In the process, the man died, and the pastor and his friends were arrested for murder. (The Indian Express 25 August 2024) There are similar incidents reported occasionally from various parts of the world.
Lack of discernment: First, a Christian should know if he is operating on human or spirit of the flesh, or by the endowment of the Holy Spirit. The pastor operated in his flesh, rather than depending on the Holy Spirit. Second, Christians should have the basic discernment of perceiving evil spirits. (I John 4:1) Discernment is also a gift of the Holy Spirit. (I Corinthians 12:10) Sadly, he became a pastor before being grounded as a disciple of the Lord.
Lack of knowledge: There are many kinds of diseases. Physical ailment through infection or lack of hygiene or genetics, illness due to stress or worry or anger or unforgiving spirit, and through attacks by Satan as Job was afflicted. (Job 2:7-10) There is a need for discernment to know which category the disease is when a person prays for the sick. All sickness cannot be needlessly credited to Satan.
Lack of preparation: When the Lord Jesus Christ descended after his transfiguration along with Peter, James, and John, there was a commotion. Other disciples were unable to cast a demon that afflicted a small boy. The father of the boy pleaded to the Lord for his intervention. The boy was instantly healed. Then the Lord taught his disciples that only by fasting and prayer, such demons could be cast out. (Matthew 17: 14-21) Probably, this pastor was not spiritually prepared.
Lack of relationship: In Ephesus, even the clothes touched by Paul were used to heal the sick and cast out demons. A Jewish high priest Sceva had seven sons, who imitated Paul. But the evil spirit said: “Jesus I know, and Paul I recognize, but who are you?” They were beaten up and had to run for life. (Acts 19: 11-16)
Have I grown in knowledge, wisdom, and faith to face Satan?