A Thelemite is someone that has attained at least one of the grades named in verse I: 40 of TBOTL.
And these grades are defined as...?
If you're having to ask that question, you can be reasonably assured that
Liber Trigrammaton,
The Book of Mutations,
the ALW system , and
Hermetic Qabalah are not the alphanumerical keys to TBOTL.
Don't get me wrong, I'm not nit-picking.
I understand; I'm aware of your sincerity, and that you're asking the hard questions that need to be asked.
Advocates of Thelema have painted themselves into a corner; those that reject the Book of the Law as a genuine divine transmission have no solid foundation to base their beliefs on other than an all-inclusive universalist philosophy that is remarkably similar to the slave religions Thelema is intended to replace, and the reason why we see people claiming that Thelema consists of the worship of Yahweh and Jesus, having nothing else to turn to but their original religious programming.
Those people that consider TBOTL genuine are having an even tougher time than their universalist counterparts, by having to exercise what is essentially faith due to the many unanswered questions that remain about verses in the book. To compound the problem, attempts to answer the questions that need to be answered are met with scorn and ridicule, or the 'shunning' dictated in
The Comment, creating a perfectly vicious circle.
The only way to answer the question about the grades effectively is by answering all of the questions TBOTL poses at the same time. To provide conclusive, comprehensive insight into TBOTL is a tremendous act of magick fraught with both dangers and complications; there is much to be gained and lost by the forces that have gathered themselves to the book, and the reason why I consider the book a magical Trojan horse. In the end, the gods of TBOTL will prevail, which is all I have to say about the matter for now.