Whether you are a Christian exercising your authority in Christ Jesus in casting out demons (evil spirits) or a psychic using mental abilities to free someone from demons, the Holy Bible warns not to rejoice in this (Luke 10:20).
Devils are only subject to the authority of Jesus Christ and He has delegated His authority to those that have received and accepted Him in their hearts and lives. In Luke 10th Chapter, Jesus indicates when we should rejoice. It's not because Christians, through the Name of Jesus, are able to cast out demons, heal the sick or do wonderful works. It's when we have a continuous relationship with Him. When we have a personal relationship with Him on a day-to-day basis, then we can rejoice because our name will be found in the Lamb's Book of Life.
There will be many Christians on Judgment Day that will tell Jesus, "We casted out demons in your name. We healed the sick in your Name." And Jesus will tell them, "Yes, but I never knew you!" (Matthew 7:22-23). Why did Jesus not know them? Because there was no relationship! And since they had no relationship with Jesus, they walked in the imagination of their own evil heart. In other words, their own way of doing things.
Therefore, let us stop rejoicing in works! But let us rejoice because our name is not blotted out of the Lamb's Book of Life! Selah.