This is a lovely topic, one I've spent the last ten years cooking on. I'll attempt to summarize what I now understand, but this understanding is always in process for me. I have done some writing about it. See Pagan Dharma-1, Pagan Dharma-2, and A Thelemic Ganachakra (a thelemic-dharma gnostic mass) elsewhere on this site.
I find when exploring a new current the guardians of the current tend to take an interest in me until I resolve my relationship to that current. This is rarely a comfortable thing.
So, my exploration of things 'Buddhist' has not been easy or gentle, but it has been very fruitful. It began simply by taking a class in seminary on "Tibetan Contemplative Tradition" along with other classes on various other religions as a way of broadening my knowledge.
It was in this class that I met Bhakha Tulku and was given the explanation of refuge "We all need help, Refuge is asking for help". For a variety of reasons this really worked for me. I'm guessing that Alobar [a list dweller] would be raising flags here about who the help is coming from and what strings are attached but I will come to that later.
While important, this understanding of refuge was not the most impactful thing I got from Bhakha Tulku at the time. It was a practice called "Benefit for Beings Pervading Space" and the reason why was because I could do it. This practice invokes Chenrezi, a.k.a Avalokitishvara, the Boddhisatva of Compassion and wields that compassion through the mantra "Om Mani Peme Hung" to remediate the suffering of the six classes of beings caught in samsara.
Samsara, some times translated as cyclical existence, is called 'Kor-wa' in Tibetan, meaning "Running in circles". The idea is that these are beings who have no control as to how they incarnate or the condition of their lives. They are entirely enmeshed in their karma and this is unsatisfactory to them. The six classes of beings benefited by this practice are Gods, Jealous Gods (called Titans by the Greeks), Humans, Animals, Hungry Ghosts and Hell Beings.
There is a lot in here that I have to gloss over but suffice it to say that the purpose of the rite is to remove some of the suffering of each of these kinds of beings in turn through the power of the mantra. Where this gets interesting is that while driving home from practice I kept finding myself filled with anger and other unpleasant emotions. And I could not get them to stop.
They became overwhelming. I was curled up in bed screaming, overloaded with all kinds of anguish and could not get my grounding. Through round about means I got a question to the Lama describing my condition and asking for advice. His reply was that I should rejoice.
Apparently it usually takes years of practice before one learns how to tie into the ground of suffering. I had done so in just a few sessions. The ground of suffering is the space or nexus of the suffering of all beings. Those who wield compassion use it to drain that domain and transform it into pleasure or power or wisdom, or whatever.
I was tying into it but I was not performing the transformation because I did not realize that the mantra was the tool with which to do the transform. Once this was explained to me, I knew exactly what to do. I wielded the mantra, fed it the suffering I was being overwhelmed with and instantly the feelings were transformed into intense pleasure and energy.
None of this was because I am in any way special. It is because I am a mage and I can work magick, like any of you.
So, I continued to study. The next big piece for me was Steven Beyer's "Cult of Tara". This work is a highly detailed study of set of Tibetan rituals. Interestingly to me, in order to explain Tibetan ritual magick, Beyer had to turn to the western tradition, in fact to all of those names we know and love. This work is for me a rosetta stone, one that showed me that the techniques of so-called oriental ritual magick are no different than those of the western tradition. It is just that their culture dedicated the same energy to ritual the west dedicated to music, so when it comes to ritual while we are playing 3 cord Rock & Roll, they are playing symphonies.
But, 'tech is tech'. The same principals used there are used here. In fact I found in this book the very method described in the Ascelepius, the brief description in the Hermetic Corpus of drawing the damon of a star into a statue to animate it. In the Cult of Tara, the statue was one of Tara, but here the full method and its theory were spelled out. I can attest to the fact that it works.
Now to Thelema. Uncle Al considered the Book of the Law as a sort of third testament. Cute, but as a student of western religion I've studied the genres of the scriptures and it doesn't quite fit. The closest thing to it is an apocalypse since it reveals something, but those usually involve some one being taken up to heaven or have a vision revealed in the temple. This one is different.
However there is a genre that very nicely matches Liber AL. In this genre a cosmology is often expressed, a specific view to practice is given and a godform is presented for the practitioner to wear. This genre is the kind of text called a tantra.
When I got exposed to the Buddhadharma I began to see Thelema in the stream of those working for the greater evolutionary purpose. It, and the rest of the western stream, the Hermetic, Rosicrucian, Alchymical, and others, I saw as part of one large process going on on this world, transcendent to any particular culture. (There have also been hints of this going on on other worlds). As I discovered the unity of western and eastern tech and so began to press on my understanding of the split, I came to realize that there was none save a historical division caused by the arisal of Islam.
In the Nyngma tradition of Tibetan Buddhism there is a peculiar version of continuous revelation. Texts, called 'termas' or treasures would be delivered to individuals who would be given the task of writing them down or figuring out how to apply them.
Pick your mythology as you will, essentially, the texts come from the fundamental ground of being out of which we all arise and which is compassionate, intelligent and provident. In its continual process of trying to help us, it creates things like tantric texts. I think Liber AL is one of these.
While Uncle Al had a hard time accepting "existence is pure joy" being a rationalist Buddhist at the time, that was mostly due to a lack of education. From the fact that in the Thoth Deck we see in the 2 of wands and the 10 of wands that he does not know the difference between a dorje and a phurba we can tell he never made contact with the Tantric or Vajrayana stream of Buddhism. This is the magick-using part of buddhism. This is also the part of Buddhism that would very well understand what is going on the in the Book of the Law, if they could only get through the code.
I'm not going to do a complete analysis here but for instance many people have trouble with the presentation of the RHK in the third chapter. However, anyone who has read the practice of a wrathful buddha would consider RHK only mildly wrathful. Stamping down on the wretched and the weak is a gentle approach to correcting suffering compared to some of the actions of the dakinis.
However this I will point out. Thelema is the first current in the west that roots itself in the Not, which the Buddhists call shunyata, poorly translated as the void. H.V. Gunther, one of the the greatest living Tibetologists today, translates it as "the sphere whose center is everywhere and its circumference is nowhere. Also, the Dharma tr. Law, is based on the awareness of shunyata and is its fundamental key, i.e., 61, 8, 80, 418, if you take my meaning.
So these are the parallels I make: Nuit is Pranjnaparamita, the perfection of wisdom embodied, Shunyata given a face and form the mother of all the buddhas (buddha means awakened one), and the basis for all refuge. Hadit is the inherent buddha nature with in each of us, already enlightened or 'perfect.' Ra-Hoor-Khuit is the union of entitative being (Hadit) and world (Nuit) and is the god form or Yi-dam for Thelemites to take in in their practice as a way or articulating their will. (Not necessarily all the time but as an archetype).
I've shared with you a refuge verse I composed on the spot previously: "In the ground of being, from which all things arise, In the inherently enlightened nature within each and everyone, In the inexorable causation the magi know, I take refuge"
If I were to spin this back around to Thelemic terminology it would be: "Nu is my refuge as Hadit my light and Ra-Hoor-Khu is the strength, force, vigor of my arms."
Now for me the proof is in the pudding. I used the methodology mentioned above and many of its components to build a set of rituals using the thelemic godforms and symbolism and used the View, the insight gained from the buddhadharms to focus it. In one of these Ra-Hoor-Khuit is the deity-form the practitioner takes on in exactly the same 'buddhist' manner. Yet the ritual is entirely Thelemic.
In this way I think I'm making Buddhism more Thelemic than making Thelema more Buddhist.
There is a lot more to all this but I will have to stop here. I am willing to answer questions. But to conclude. . .
For me there is that which lies beyond all of our cultural view points that drives all sentient beings towards their complete happiness. The Buddhadharma and Thelema are two manifestations of this same source and as such have harmonious union.
I took refuge to make peace with the guardians of the Buddhadharma, to further commit myself to the great work of bringing happiness to all beings, and to unite within myself two approaches to the same goal.
For me, I have one life, thus one path, and I find value in uniting in that path the truth however and where ever I find it.