Acts 19:13

Acts 19:13 - 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.”

As we continue on in this story we see that these men were not always successful in driving out evil spirits. In fact their situation got really bad, really quick, when one of the spirits answered them. It said, “Jesus I know, and I know about Paul, but who are you?” After saying that the possessed man proceeded to beat them until they ran out of the house naked and bleeding.
These men saw the power of God flowing through Paul and they wanted to take part of it. Basically they bypassed getting to know God and went straight to doing miracles. This was their mistake. They were able to cast some evil spirits out, but eventually it caught up with them.
In their mind it was ‘Paul’s’ God and not their own. They never got to know God and therefore God did not know them. Jesus warns us that on ‘that’ day there will be many who come and say, “Did we not do miracles in your name? Did we not cast out demons?” And Jesus will answer, “Depart from me, I never knew you.”
Don’t let that be you. Get to know Jesus. Spend time with Him and spend time in the Word. It’s not about ‘the Jesus Paul preaches.’ You must know Jesus yourself, then when you do miracles in His name it is personal and powerful.