Unclean demons and spirits possess a person by taking control and subduing the subject. They must be cast out of the possessed as Jesus did in his days on earth. On the other hand, the Holy Spirit of God enters us only with our permission and leaves us when we reject him. He fully respects our free will and never tries to gain control of us. He only inspires, uplifts, and purifies us, empowering us to live a holy life in freedom.