This is not an exhaustive treatise on the [Catholic] spiritual life, but rather an outline which may serve as the basis for deeper study. However, in order to avoid the dryness of a mere outline it was deemed necessary to develop the most important points of the spiritual life, such as, the indwelling of the Holy Ghost in the soul, our incorporation into Christ, the role of the Blessed Virgin in our sanctification, the nature of Christian perfection and the duty of striving after it.