The Witch's body houses his soul. Witches who believe in reïncarnation - and most do - regard earth as a place of learning. Their time on this planet is spent gaining and applying knowledge in ways that can only be accomplished on the physical plain. The eventual goal, however, is to stop the cycle of reïncarnation so the soul can return to the Source (Yog-Sothoth).

How long a soul waits between incarnations is uncertain. Several years, or perhaps decades or centuries, may pass between sojourns in this world. 

You may have a specific "task" or "reason" for assuming a particular lifetime. Karmic issues incurred during previous existences influence your present and future lifetimes. Consequently, your soul might have to wait until conditions on earth are optimal for you to undergo the spiritual growth you seek before you can re-enter a physical form.