What are Thelemites?
Do what thou wilt shall be the whole of the Law.
Who calls us Thelemites will do no wrong, if he look but close into the word. For there are therein Three Grades, the Hermit, and the Lover, and the man of Earth. Do what thou wilt shall be the whole of the Law. Liber AL I;40
A Thelemite, briefly, is a person who accepts "Liber AL", The Book of the Law, as the fundamental statement of doctrine and belief, and who tries to live life by the principles established in it. Those principles establish the individual's absolute freedom, so long as we act in accordance with our "Will". Our duty and our challenge, then, is to discover and do our Will:
So with thy all; thou hast no right but to do thy will.
Do that, and no other shall say nay.
For more information on Thelemic theology, there is a good article at the OTO USA web site. Part of that article is well worth quoting here:
Thelema considers any action which is not directed toward the discovery and accomplishment of the True Will to be "black magic". This includes acts of interference with any other individual's lawful exercise of their right to discover and accomplish their own True Will. Thelemic doctrine holds that the disharmony and imbalance created by such actions results in a compensatory, equilibrating response from the universe; a doctrine similar to that of the Eastern conception of "Karma".
We have the right to discover and do our own Will without interference from others, and so does everyone else. This is somewhat similar to US Supreme Court Justice Oliver Wendell Holmes' statement that "The right to swing my fist ends where the other man's nose begins." Aleister Crowley's Liber OZ also gives insights into our rights when doing our Will.
But, what is our Will? How will we know it when we find it? That's a subject that fills volumes, and can — in fact, should — take an entire lifetime to figure out.
Love is the law, love under will.