"So then is sin, for a magician, to ignore or repress that yearning to express their will?"
It's a good question. So it gets a full post essay on the Sins of a Magician.
Crowley said the "word of sin is restriction" in the Book of the Law. That one gets quoted a lot, even though it's talking about fucking, really, and fucking a lot the way you want to, in context, because fucking is cool.**
Sin is a useful concept within religious thought. In my Chrsitian (Protestant, Calvinist, Puritanical) system, "Sin" is any act that keeps you away from God. Applying that to Hermetics, yeah, ignoring and repressing the yearning to express your will is sinful. Not expressing your Will obviously keeps you away from God, right? It's not doing it right, it's doing it wrong, it's bad. It's evil. It's sinful.
Sin implies a punishment, because it's been used as a means to control people instead of as a means to bring them spiritual enlightenment. Folks who did this had less interest in having an enlightened populace than a terrified one. Whatever, the use of the concept of "sin" to control instead of inspire has rendered it pretty useless.
People don't understand that "sin keeps you away from god" is the total punishment itself. Being away from God sucks. You can only know that if you've been around him though, and it doesn't make as much sense to folks who haven't felt the presence of god personally loving them up as it tumbles around you, in you, through you to bounce laughing out your vocal chords.
And really, think about it. Can magicians sin? I've explained that we're beyond good and evil, right? I meant it. I'm serious when I say that shit. I can give you several applicable soteriologies from my Hermetic belief, if you want to know why sin doesn't exist for us.
The folks who did the Seven Spheres in Seven days with us got a taste of exactly what I'm talking about, though. That was pretty awesome. They tasted the powers of the planetary spheres, the forces of creation. They experienced these powers. They felt them flow. They got a hint that they are all gods put here on earth to manifest their reality. They remembered collectively that they are visiting gods from other worlds here on individually missions of extremely sensitive personal import.
There's no sin, magicians. There's just what you do. Do what thou wilt shall be the whole of the Law. That's it, that's the Law. There's just what you Do, what you Will. There ain't no middle ground. Those things are one thing, Do/Will. What you DO... that is what you fucking WILL.
So what kind of god are you? A shitty mean small minded ignorant one? A benevolent force of joy and wealth? A frenzy of illuminating madness spreading amongst all who touch the hem of your garment?
You are expressing your will all the time, in everything you've ever done, in everything you ever do, everywhere you've ever been, everywhere you're going to. ***
Magic teaches us to do it better. We learn who we are by observing what we do. We do things to get what we want. Sometimes the stuff we do works, sometimes it's broken. We learn to fix the things we do that don't get us what we want, we change our approach using the wisdom, techniques and powers of the forces of manifestation. We learn to be ourselves better, more intentionally by becoming aware of what we're doing.
* If you don't recognize the title reference, click the link, you poor unfabulous person.
** Just wanted to point that out to the Crowley haters... You hate a guy who wrote a holy book about how cool it is to fuck. Seriously. Think about that some time.
*** Awww yeeeeeahhhhh!