One of my favorite books by Dr. Ernest Holmes is This Thing Called You. In the book, he talks about believing there is a Spirit within us, whether we understand it or not, which forever exists; it always has, it does now, and it always will.
Visualize this Spirit as an oil lamp that is controlled by our thoughts, our beliefs and our feelings. It can be turned up or it can be turned down; but it can never be shut off. Through free will, we each experience Spirit to our level of faith and acceptance.
Knowing this, why do we sometimes seem to not shine brightly? Why do people stay in abusive relationships? Why do alcoholics continue to drink? Sometimes we are comfortable in the familiar, even when it does not support our highest good. Sometimes the oil lamp is turned down so low that we forget our connection to Spirit, that Thing-Behind-All-Things.