This is a good question. Jesus referred to the casting out of demons as Children’s bread, referring to those who are in covenant with God. Those who have not accepted Jesus as their Lord and savior, are not children of God, and have no covenant with Him.
Matthew 15:26, “But he answered and said, It is not meet to take the children’s bread, and to cast it to dogs.”
If light cannot dwell with darkness, and all darkness leaves a believer’s life when they become a Christian, then why do we still have evil thoughts, desires, feelings, and bondages to lust, pornography, anger, etc. long after we accept Jesus? This is a very good question. Is there anywhere in the Bible which tells us that some darkness can remain, while other types of darkness is automatically shed at the time of salvation? No, it does not. If light could not dwell with darkness, then Paul couldn’t have had both the Holy Spirit, and evil present in him at the same time, as we can see in this passage:
Romans 7:20,21, “Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me. I find then a law, that, when I would do good, evil is present with me.”
Why is authority required to cast out demons, if they leave on their own the moment their legal rights are removed? It is through our authority in Christ, that we are able to drive out demons. Why did God give us this authority, if what we should really be doing is simply winning souls for Jesus?
Mark 1:27, “And they were all amazed, insomuch that they questioned among themselves saying, What thing is this? what new doctrine is this? for with authority commandeth he even the unclean spirits, and they do obey him.”
Persecution Live 