God created the soul pure, simple and clean of all stain of sin, with a certain beatific instinct towards Himself whence original sin, which the soul finds in itself, draws it away, and when actual is added to original sin the soul is drawn yet further away. The further it departs from its beatific instinct, the more malignant it becomes because it corresponds less to God.
St. Catherine of Genoa, The Treatise on Purgatory