Acts 19:13-16 - Let Jesus Take Care of Your Demons.

Acts 19:13-16 (NIV) Some Jews who went around driving out evil 
spirits tried to invoke the name of the Lord Jesus over those who were 
demon-possessed. They would say, "In the name of Jesus, whom Paul preaches, I 
command you to come out." 14 Seven sons of Sceva, a Jewish chief priest, 
were doing this. 15 [One day] the evil spirit answered them, "Jesus I 
know, and I know about Paul, but who are you?" 16 Then the man who had 
the evil spirit jumped on them and overpowered them all. He gave 
them such a beating that they ran out of the house naked and 
bleeding.  

Many Ephesians engaged in exorcism and occult practices for 
profit (see Acts 19:18,19). The sons of Sceva were impressed by Paul's 
work, whose power to drive out demons came from God's Holy Spirit, not 
from witchcraft, and was obviously more powerful than theirs. They 
discovered, however, that no one can control or duplicate God's power. These 
men were calling on the name of Jesus without knowing the person. 
The power to change people comes from Christ. It cannot be tapped by 
reciting his name like a magic charm. God works his power only through 
those he chooses. [Life Application Study Bible re Acts 19:13-16] 

What The Bible Says - Demons
Ephesus was a center for black magic and other occult practices. 
The people cooked up magical formulas in search of wealth, 
happiness, and fertility. Superstition and sorcery were commonplace. Many 
Ephesians engaged in exorcism and occult practices for profit. The sons of 
Sceva were impressed by Paul's work, whose power to drive out demons 
came from God's Holy Spirit, not from witchcraft, and was obviously 
more powerful than theirs. They discovered, however, that no one can 
control or duplicate God's power.  
One of Satan's schemes is to make demonically influenced 
activities seem normal, commonplace, or even "good." Even today, demonic 
activities are masked as harmless fun, and too many people are falling for 
it. Christians have no business going to fortune-tellers, putting 
trust in horoscopes, channeling people who lived long ago, or getting 
involved in Wicca activities and casting spells. God clearly forbids such 
practices (Deuteronomy 18:9-13, April 1). Moreover, they are harmful to 
the soul. There's no fooling around when it comes to Satan. [The One 
Year Bible for New Believers re Acts 19:13-20] 

Who Are You?
There is no secondhand spirituality. No one else can develop 
Christian maturity on your behalf. A strong Christian heritage is an 
asset, but it cannot take the place of your own vibrant, growing 
relationship with Christ. 
Paul had a powerful walk with God. God used him so mightily that 
extraordinary miracles occurred through his life. Cloths that touched Paul 
were taken to the sick, and the sick were healed (Ac 19:10-12). Evil 
spirits were cast out. Paul's preaching and teaching were instrumental 
in building a strong church in Ephesus. Paul's ministry was so 
impressive, in fact, that others tried to duplicate it. 
Seven sons of the chief priest, Sceva, attempted to cast out 
demons the way Paul did. They confronted an evil spirit and attempted 
to exorcise it "by the Jesus whom Paul preaches." These men were 
trying to use a spiritual power that Paul had acquired after years of 
walking closely with his Lord. They could imitate Paul's words, but they 
could not duplicate the power that was his through his personal 
relationship with God. The evil spirit retorted, "Jesus I know, and Paul I 
know, but who are you?" The demon then viciously attacked them and 
humiliated them. The evil spirits were fearfully aware of Jesus (James 
2:19); they were familiar with Paul's influence over the powers of 
darkness. But the demons had no knowledge of the seven sons of Sceva. 
You can duplicate the words and deeds of a spiritually mature 
Christian, but you cannot inherit his or her walk with God. Christian 
maturity takes effort; it comes over time. If you ignore the place of 
prayer and if you neglect your relationship with Christ, you will not 
grow in your faith. Imitating the faith of others will not give you 
victory. Only as you nurture your own relationship with Jesus will your 
life be filled with spiritual maturity and power. [Experiencing God 
Day by Day by Henry and Richard Blackaby re Acts 19:15]