Let's say for example, you owned a restaurant and you hired a chef and gave him the responsibility of cooking. Now customers come to your restaurant to eat, but when they order food, nothing is available because the chef didn't cook and the same chef comes running to you and say, "why didn't you cook". Wouldn't you think he is nuts, you would obviously say "that's what I hired you to do". And the chef says "but its your restaurant", "yes it is my restaurant but I delegated the kitchen to you".
This is what happens with many people, they want God to do what is actually their responsibility. If a demon was oppressing you, and you ran to God to cast him out for you, God's response would be that's not my department.There is nowhere in the Bible where it says God will cast demons out, but there is where it is says human beings shall cast demons out in the name of Jesus. "And these signs shall follow them that believe; In my name shall they cast out devils;" (Mark 16:17). Instead of telling God, you say to the demon "go" and he will go. God the Father has given Jesus, a name which is above every name and "at the name of Jesus, every knee, should bow, of things in heaven and of things in the earth and every tongue confesses that Jesus is Lord" (Phil 2:10). Now this name has been given to us as power of attorney, this means when we speak in his name, everything will respond to us as it would to Jesus. When you say in the name of Jesus, your words become the words of Jesus because you are speaking in his place. In his name we command miracles to happen and they happen Alleluia, we say to the sick be healed and they get healed, to the dead we say arise, and they come back to life.