John Paul II put his finger on a problem typical of our time, namely, that people think that they can do lots of bad things while still remaining, deep down, “good persons,” as though their characters are separable from the particular things that they do. In point of fact, a person who habitually engages in self-absorbed, self-destructive, and manipulative behavior is slowly but surely warping her character, turning herself into a self-absorbed, self-destructive, and manipulative person. Viewed from a slightly different angle, this is the problem of separating “self” from the body, as though the “real person” hides under or behind the concrete moves of the body. Catholic philosophy and theology have battled this kind of dualism for centuries, insisting that the self is a composite of spirit and matter. In fact, it is fascinating to note how often this gnostic conception of the person (to give it its proper name) asserts itself and how often the Church has risen up to oppose it.
an excerpt from an article on The Integrated Catholic Life blog by Father Richard Baron