The Will is completely central to Thelema. Liber AL vel Legis, the central text of Thelema states:

Do what thou wilt shall be the whole of the Law. (I:40)
Thou hast no right but to do thy will. Do that, and no other shall say nay. (I:42-43)
There is no law beyond Do what thou wilt. (III:60)

There are two “planes” that one must consider the Will on for it to be understood completely. The first plane will be labeled the “theoretical/absolute” and the second will be labeled “practical/relative.” As Aleister Crowley warns in many places we are not to “confuse the planes” – that is, we must keep the considerations of each plane within its own sphere and not let the judgments that pertain to one be confused as pertaining to the other.

On the theoretical/absolute plane, everyone and everything is already doing its “true” or “pure” Will.

“There are much deeper considerations in which it appears that ‘Everything that is, is right’. They are set forth elsewhere; we can only summarise them here by saying that the survival of the fittest is their upshot.” — Magick in Theory and Practice, Chapter I

“The uninitiate is a "Dark Star", and the Great Work for him is to make his veils transparent by 'purifying' them. This 'purification' is really 'simplification'; it is not that the veil is dirty, but that the complexity of its folds makes it opaque. The Great Work therefore consists principally in the solution of complexes. Everything in itself is perfect, but when things are muddled, they become 'evil'.” –New Comment to AL I:8

“…Each of us stars is to move on our true orbit, as marked out by the nature of our position, the law of our growth, the impulse of our past experiences. All events are equally lawful - and every one necessary, in the long run - for all of us, in theory; but in practise, only one act is lawful for each one of us at any given moment. Therefore Duty consists in determining to experience the right event from one moment of consciousness to another.” –Intro to Liber AL, part III

This last quotation touches on the pertinent issue of this short essay: “All events are equally lawful – and every one necessary, in the long run – for all of us, in theory.” This is the Will perceived from the theoretical/absolute plane – Crowley himself uses the terminology of “in theory” to describe this aspect. In an “absolute” sense, or from an “absolute” perspective, “all events are equally lawful – and every one necessary.”

He then writes, “but in practise, only one act is lawful for each one of us at any given moment… Duty consists in determining to experience the right event from one moment of consciousness to another.” This is the Will perceived from the practical/relative plane. In a relative sense, there is discrimination needed.

The first and most common “confusion of the planes” occurs when one perceives the truth of the theoretical/absolute plane of Will. In this sense, all events are lawful and necessary and there is no “wrong” or “evil.” This means in the world that no actions are to be restricted whatsoever because all things “work out in the end,” you might say. This will literally be the death of you if one decides to adopt the theoretical/absolute perspective as a practical/relative philosophy. Although the Will is “perfect” and “necessary” on the theoretical/absolute plane, there is a “Duty” that is the practical necessity of determining the action that is “right.”

The theoretical/absolute plane of Will is virtually useless on a practical level, although knowledge of the fact that Will cannot truly ever err may give rise to a certain confidence, detachment, and carefree attitude. It is on the practical/relative plane of existence that we normally function on, therefore a practical/relative understanding of Will is needed.

In Thelema, the practical/relative application of this is stated as:

Love is the law, love under will. (I:57)

Love is the modus operandi of the Thelemite, and it must be “under will.” “Each action or motion is an act of love, the uniting with one or another part of ‘Nuit’; each such act must be 'under will,' chosen so as to fulfill and not to thwart the true nature of the being concerned.” (Intro to Liber AL, part III)

Therefore, the Will of Thelema must be considered as simultaneously operating on two planes: the theoretical/absolute and the practical/relative. On the plane of the theoretical/absolute, all events are perfect, pure, & necessary; on the plane of the practical/relative, the Thelemite operates under the formula of “love under will,” assimilating experience in accordance with their unique nature.