This is the first of two volumes dealing with the mystery of our spiritual constitution, the approach to that mystery and the description of Divine events within the Soul. We are told how our spiritual constitution is mirrored in the physical form, its wonderful organs and its realm of heart and mind -- even its substances being an accommodated form of spiritual substance. Every part of the physical vehicle corresponds to a higher function in the spiritual vehicles through which we also live. So, in searching for the inner reality, the Spirit or Life-stream, which is love in its dual flow, is able to move with increasing freedom through the substance of all our vehicles. Thus love becomes embodied in Life. This is the mystery of which the Mass speaks, an inner reality, a continuous process wherein the life of Love takes form.