Soul and spirit are used interchangeably, but are not exactly the same. Here's a definition of "Soul."

SOUL The spiritual, rational, and immortal part in man; that part of man which enables him to think, and which renders him a subject of moral government; -- sometimes, in distinction from the higher nature, or spirit, of man, the so-called animal soul, that is, the seat of life, the sensitive affections and phantasy, exclusive of the voluntary and rational powers; -- sometimes, in distinction from the mind, the moral and emotional part of man's nature, the seat of feeling, in distinction from intellect; -- sometimes, the intellect only; the understanding; the seat of knowledge, as distinguished from feeling. In a more general sense, "an animating, separable, surviving entity, the vehicle of individual personal existence." Tylor. "The eyes of our souls only then begin to see, when our bodily eyes are closing."
Energy; courage; spirit; fervor; affection, or any other noble manifestation of the heart or moral nature; inherent power or goodness.
A human being; a person; -- a familiar appellation, usually with a qualifying epithet; as, poor soul.
A pure or disembodied spirit.