The Middle Pillar Ritual was an original Golden Dawn exercise, championed in the work of Israel Regardie, and which remains very popular today as various permutations of the practice exist within many magical curriculums.
Exoterically, the performance of the middle pillar exercise is an assistive practice which facilitates the raising of energy within the esoteric bodies.
In the official Golden Dawn instructions the exercise is described as “a magical ritual of self-initiation”, “a process of uniting human consciousness with divine consciousness”, a “dynamic method of the Great Work itself”.
“To my mind, the exercise described as The Middle Pillar is the groundwork of all actual developmental work. It is a process which is the basis of magic. That this has been but seldom realized is obvious at the root of futile attempts to do ceremonial and perform ritual, of which the general public hears every now and again. Even students of magic of many years standing have been guilty of negligence in this respect, and also in failing to recommend it to their successors.” – Israel Regardie
During the podcast you’ll find a short introduction to The Middle Pillar exercise including an interesting commentary on the uses of the exercise, including some tips for integrating the exercise into other Thelemic practices.
This podcast is very useful as David walks through the accurate pronunciation of the names of the sephiroth and includes commentary which will help with the establishment of the correct mental attitude relevant to the performance of the exercise.
You can find original Golden Dawn instruction on the Middle Pillar exercise here: http://thelemicgoldendawn.net/neophyte/mpeinstruction.htm
You can download the .pdf of Israel Regardie’s book “The Middle Pillar”, which includes the most complete exposition of the exercise here: http://www.golden-dawn.com/eu/UserFiles/en/file/pdf/Middle_Pillar.pdf