Tony de Mello was a psychologist and writer. And more than that he was catholic, a jesuit, a poet and a mystic.
When you read his books you have to bear in mind that his spiritual experience and teachings are based and focused from these facts: that God surround us in nature, that spirituality is a multi layered experience, that people are complex, and the "Spiritual Exercises" that culprit of spirituality written by San Ignatius of Loyola, .
Thus, Sahdana is a happy mixture of both indian spirituality (meditation, yoga, pantheism) and christian contemplation (God and Jesus as the center of every experience. All in all, it is a deep exercise of religious dialoge, in which religious people can gain from each other's beliefs and richness, not wanting to convince or overwhelm the other.
Sahdana is a way to perfection, to fulfillment, because it gives a clue to oneself.
. It's a book on christian spiritual growth, but I think others can benefit from its lecture and use, if they make some little exceptions due to the basic catholic background.
This is not a book for "self improvement" in a marketing short of way, nor a "new age" book, but a rich life experience.