The Course of The Spiritual Life

The whole course of the spiritual life is falling off, and returning, slipping away from the truth and turning back to it, leaving and returning. (Henri Nouwen, Home Tonight: Further Reflections on the Parable of the Prodigal Son, p.41)

This is a common theme in Nouwen’s writing.  Is that what you believe?  Or do you think, as I typically have but maybe in error, that the spiritual life is a gradual improvement, where the “falling off” and “leaving” lessen over time?  More to the point, which of these two do you actually experience in your spiritual life?