Here’s an interesting quote by William Walker Atkinson:

“Of all the mental faculties or powers, that of the Will is the closest to the “I” or Ego of the person. It is the Sword of Power clasped in the hand of the Ego. One may divorce himself in thought from the other mental faculties and states, but when he thinks of the “I” he is bound to think of it as possessing that power which we call Will. The Will is a primal, original power of the “I” which is always with it until the end. It is the force with which he rules (or should rule) his mental and physical kingdom – the power of which his Individuality manifests itself upon the outside world.

Desire is the great motive power inciting the Will to action in life. As we have shown you the action of Will without the motive power of Desire is unthinkable, and therefore it follows that the culture and right direction of Desire carries with it the channel of expression and manifestation of the Will. You cultivate certain Desires, in order that the Will may flow out along these channels.

By cultivating the Desire along certain lines, you are making channels along which the Will may flow in its rush toward expression and manifestation. So be sure to map out your Desire channels clearly by making the proper Mental Images of what you want – be sure and make the Desire channels deep and clear-cut by the force of repeated attention and autosuggestion.

History is filled with examples of men who have developed the use of the Will. We say “developed the use” rather than “developed Will,” for man does not develop his Will – his Will is always there ready for use – a man develops his ability to use the Will – perfects himself in its use. We have frequently used the following illustration, and have not been able to improve upon it: Man is like a trolley car, with the upraised trolley-pole of his mind reaching out to the live wire of Will. Along that wire is flowing the current of Will Power, which it “taps” and draws down into his mind, and by which he is able to move, and act and manifest power.

But the power is always in the Wire, and his “developing” consists in the ability to raise the pole to the Wire, and thus “tap into” its energy. If you will carry this idea in your mind, you will be able to apply this truth more easily in your everyday life.”