This Prâna (spirit) is born of the Self. Like the shadow thrown on a man, this (the prâna) is spread out over it (the Brahman). By the work of the mind does it come into this body.

In plain words: The teacher says Prana, the life-force, comes from the Self, the deepest reality. It follows the Self the way a shadow follows a person. It enters the body because of the mind's past thoughts and actions.