Years ago I witnessed an unexpected "tongues outbreak" by a fellow employee who was a member of an evangelistic church. He was loudly calling on Jesus and speaking words nobody knew. Everyone in the work area was startled! After my break I had to walk past the tongues-speaking employee to get to my work area. As I came near him the hair on the back of my neck stood up and I started to get goose bumps! Because I was becoming very uneasy I quickly went by the fellow worker. Did he have an evil spirit (demon) or had he worked his mind into a state of confusion? I wasn't sure what was the REAL cause of the tongues but I do know, based on the person's religious beliefs, that even if he HAD a demon it was doubtful he would want it cast out!
Interestingly, just BEFORE Matthew's account of the disciples' inability to cast out a demon, Jesus had sent them on a "gospel training mission" to some cities. Before they left Jesus gave them the authority to heal the sick, raise the dead and cast out demons wherever they went (Matthew 10:5-15).
Another interesting thing to note is that initially the demon in Matthew 17 could not be cast out not only due to a lack of faith on the part of the disciples but also the FAITHLESSNESS of those around the demonically-possessed person:
"Then Jesus answered and said, 'O FAITHLESS and perverse generation, how long shall I be with you? How long shall I bear with you?'" (Matthew 17:17)
It was only after the disciples failed and the crowd was chided for their faithlessness that Jesus rebuked the demon.
These scriptures warn us that just because someone (including ourselves) believe in Jesus or uses Jesus' name does not mean they (or we) have the faith and authority from God to command spirits. Casting out demons is serious business and not to be taken lightly. Anyone taking on themselves the driving out of demons had better be well grounded in the scriptures and have an ample portion of God's Holy Spirit! Those who wrongly ASSUME they have the power and authority to cast out demons can suffer some very real painful consequences, as the following Bible verses describe:
"Now God worked unusual miracles by the hands of (apostle) Paul, so that even handkerchiefs or aprons were brought from his body to the sick, and the diseases left them and the evil spirits went out of them.
"Then some of the itinerant Jewish exorcists TOOK IT UPON THEMSELVES to call the name of the Lord Jesus over (assuming the authority of Jesus) those who had evil spirits, saying, 'We exorcise you by the Jesus whom Paul preaches.' Also there were seven sons of Sceva, a Jewish chief priest, who did so." (Acts 19:11-14, emphasis added)
Those who were claiming the ability to cast out demons were sons of a Levite chief priest. Because of this, they must have thought of themselves as being pretty important and powerful, certainly powerful enough to simply assume they could use the name (authority) of Jesus Christ (after only hearing of Him through the apostle Paul) to cast out demons.
There was, however, one problem. These men believed all they needed to do was use the name of Jesus, kind of like a magican who says some "magic words" before a trick like ABRACADABRA, and then, PRESTO, what they wanted to happen would occur! The problem was the demon(s) they were trying to cast out of a person KNEW the true power it took to FORCE them to leave and KNEW these men were ultimately only PRETENDING that they had it! Ironically, the men trying to act like they were God were in reality DECEIVED, while those whose existence was based entirely on DECEPTION (demons) knew what was the REAL truth!
The demonic response to the presumptuosness of the men was swift and to the point:
"And the evil spirit answered and said, 'Jesus I know, and Paul I know; BUT WHO ARE YOU?' " (Acts 19:15)
The demon not only gave the men a verbal chastisement, but went on to inflict physical HARM on those who acted so foolishly:
"Then the man in whom the evil spirit was leaped on them, overpowered them, and prevailed against them, so that they fled out of that house naked and wounded. This became known both to all Jews and Greeks dwelling in Ephesus; and fear fell on them all, and the name of the Lord Jesus was magnified." (Acts 19:16-17)
Those who saw or heard of what happened quickly learned not to take the name and authority of Jesus Christ lightly --- and especially not to ASSUME they had God's authority to do whatever they pleased. If God has not ordained you to use His name to cast out demons, do not think you can simply conjure up some faith and do it anyway. It will not work!