God created man with three distinct parts-–– a body, a soul and a spirit.  Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ. (1 Thessalonians 5:23).  The body, the soul, and the spirit serve distinct purposes and are part of the intentionality of God in creating man this way.  

Body: The body hosts both your soul and your spirit.  The body (sóma) was formed out of the dust of the earth and is compatible with the physical world, and like the physical world it is temporary.  The life that He placed within the body is called bios.  

Soul: The soul (psuché) was created to establish an understanding and an interaction with the created world.  The soul governs the actions of the body and the soul is meant to be informed by and obedient to the spirit.  The fall destroyed this balance and allowed the soul to act independently of the spirit.

Spirit: God imparted a spirit to man (pneuma) from His own person. The life of the spirit is called zoë, it is the exact life that is in God and it is eternal. This life does not require the creation for its support, it is maintained Spirit to spirit.  The zoë life of God is available and imparted when the spirit of a person is activated and becomes aware of God for the first time in their life. You receive an understanding of God Himself and the ability to receive revelation which transforms your understanding and your wisdom from the carnal, sensual, and the devilishly sourced to that which is pure and from God.  But you can actually live in your body, within the life of your soul, and interact with creation without the life of your spirit ever being activated.  

No evil spirit has access or entrance into the sacred, inner sanctum of your spirit being. They cannot live where the Holy Spirit lives but they can live where they are given access.  A human being, even a believer in Christ, can unwittingly give access to a demon through their soul.  An evil spirit cannot dwell where the Spirit of God dwells, in your spirit, but they can dwell in your soul.  Your emotions live in your soul and the capture of your emotions is where evils spirits are able to achieve control, which in turn allows them to inhabit the soul. When they do, you do have fully active demonic capabilities functioning in your soul, manifesting in human behavior, in the human body.  

For further study on this subject see the complete series, Blockage Removal Training, found within the branch: Healing The Soul From Trauma.