Mark 3:14-15 (TPT) (Jesus) wanted them to be continually at His side as His friends, and so that He could send them out to preach and have authority to heal the sick and to cast out demons.
Pulling down the strongholds of Satan is an integral part of the Great Commission (II Cor. 10:4). We need not fear the darkness. Christ gives us power (the dynamic of expulsion) and authority (the right to use His power—as if He, himself, were doing it). We are in a real warfare against darkness. Our prayers are powerful. Be filled with the Holy Spirit every day so that you will be fully equipped.