The Rite of the Qabalistic Cross
The Qabalistic Cross is often considered to be no more than the preamble and afterword to the LBRP (a ritual that is often itself not entirely understood or appreciated), with most people little realizing the tremendous potential of so humble a ritual. While it is true that many esoteric books give detailed instructions on the formula of the rite (vibrate the traditional words while tracing and visualizing a cross of white light extending from a sphere of light above one's head to another below one's feet and out others at either of one's shoulders to the ends of the universe), such books never seem to concern themselves with the significance of all this personal theater.
This ritual is not merely an exercise in visualization, but is both a drawing down of LVX from Kether (the aforementioned ball of brilliant white light one visualizes above one's head) through the entire Middle Pillar to Malkuth, out to both Gevurah and Chesed, and a circulating of said LVX through the whole of the magician's sphere of sensation, or energetic body.
One of the places in which such instructions fail is that they typically do not mention the significance of drawing the LVX down past Da'ath in the throat to the rest of the Middle Pillar. Just as Da'ath forms a veil or barrier between the Supernals and the rest of the sephiroth (and between Atziluth and the other qabalistic worlds) in the macrocosmic Tree of Life, so does it form a barrier between these levels of the microcosmic Tree within each individual's sphere of sensation. This barrier must at all costs be breached; otherwise little benefit will be gained from the practice. In the Golden Dawn, the word "Atah" is split, with the first syllable being pronounced at Kether and while the shaft of LVX is being drawn down to the throat, while the second syllable is pronounced at Da'ath to signify bringing the LVX through the barrier of the non-sephirah.
The process of invoking and circulating LVX throughout the sphere of sensation energizes the whole of the Tree of Life as it exists within the microcosm of the magician's energetic body, circulating out stale energy and replacing it with fresh LVX, whilst simultaneously both feeding and strengthening the practitioner's energetic body. The effect on the energetic body is akin to the combined effects of proper diet and exercise on the physical body. The Qabalistic Cross is a means of "enflaming oneself with prayer," and the influx of LVX from Kether bestows upon the magician both the energy and the authority to perform the remainder of his rituals (it is chiefly through the practice of rituals such as this that one comes to truly realize that one is God, and that one bestows such authority on oneself, contrary to many Old Aeonic ways of thinking).
In the final analysis, it is the cumulative benefit to the energetic body of the magician that is the most significant aspect of this ritual. Frequent and faithful practice of the Qabalistic Cross strengthens and develops the Lunar body, which is the energetic or astral body with which we are all born. In most people, the Lunar body is weak and under-developed. A healthy energetic body is not only essential to successful magickal practice, but also to psychological and spiritual health in general, and can also have a pronounced effect on one's physical health.
Further, it is from the Lunar body that the Mercurial body is developed, and from the Mercurial body that the Solar Body is developed. The development of these two energetic bodies is part and parcel of the evolutionary and alchemical process of the Great Work. The development of the Mercurial body can only occur, however, from a healthy and well-energized Lunar body. To use an analogy, the Qabalistic Cross both plants the seeds of the Mercurial body and fertilizes the soil in which those seeds are planted. Thus, the Qabalistic Cross can be accurately thought of as one of the primary foundations of the Great Work.