In the meantime you’ll get a messy meta from me, i’m not going back for specific quotes/page numbers rn but here we go:
At first the idea of Simon being immune to magic seemed really tragic to me - another degree of separation between him and Baz and Penny and the whole World of Mages. But the more I’ve thought about it the less I see it that way.
I think for me it comes down to the fact that magic, in relation to Simon, was always a weapon. It was weaponized against him through the Humdrum and the Mage, just as much as it was a weapon he wielded. Magic was used against Simon from literally the moment of his conception; he was created and born and raised as a magickal weapon. He should have had magic that was just his own, his birthright, but because of the Mage magic was always something that was done to him as much as it was a part of him.
We know Simon misses his magic, misses it like a phantom limb, and at first his magickal immunity seems like another form of loss. But I don’t think it is. Simon losing his magic directly affected what he could do; becoming immune to magic directly affected what could be done to him. That immunity immediately puts him that much further out of the reach of people like Smith Smith-Richards. We see this really clearly in the chapel scene, when Simon is able to withstand the onslaught of hundreds of spells directed at him. He charges into the Chapel knowing he’s safe, and that he’s able to keep Baz and Penny safe by extension. In that scene, his immunity looks a lot less like a tragedy and a lot more like a superpower.
The fact that this happens in the Chapel, the same place where Simon killed the Mage, is probably the most important detail. There’s a direct parallel between the “spell” Simon casts that kills the Mage - “Stop hurting me!” - and the fact that Smith’s/the other mages’ magic literally can’t hurt him. I think it’s symbolic of his healing, of a cycle being closed.
But the person who gives Simon his immunity is the Big Bad of the book! How can healing come from the villain?
Well, yes, but Smith-Richards is also clearly a foil for Simon. Through Smith-Richards, I think Simon is finally able to see how destructive and toxic the Chosen One role he was forced into is; seeing how Feverfew manipulated Smith maybe gives him some insight into how the Mage manipulated him. At the beginning of AWTWB, Simon asserts that nobody used him - at the end, he admits to himself that the Mage used him, turned him into his boy soldier. Through Smith, Simon is able to comprehend and feel part of the immense damage done to him, and by confronting and ultimately defeating Smith he symbolically confronts and begins to move beyond certain aspects of his own trauma. Therefore I see the fact that Smith casts the spell that gives Simon his magickal immunity as a sneaky way of figuratively showing Simon healing himself and giving himself the tools to work through his trauma.
Simon’s magickal immunity is a hard boundary being placed. Throughout the book (and the series) Simon and other characters repeatedly mention how uncomfortable Simon is with having spells cast on him. He specifically asks that spells not be cast “on my body” and only allows for very particular exceptions. It’s not a coincidence that his immunity prevents spells from being cast on his body. Things on or around him can still be magickally affected - his shirt can fit like a glove, for instance - but his physical body is beyond the reach of magic. It is solely under his control and power. I can only imagine how good that would feel, after finally realizing how much harm has been done to him, to know that his physical body is protected that way! Simon also clearly states that he doesn’t want Penny to keep trying to find a way to reverse his immunity; he clearly prefers having it to not having it, so I think it’s safe to say that the immunity gives him some measure of comfort!
Magic was always a weapon in relation to Simon. It was a weapon used against him over and over and over again, until it couldn’t be used on him at all. It was also a weapon that Simon wielded, but never felt fully comfortable with. He could never control the chaotic, explosive magic that the Mage forced him to carry, and he was always more adept with his sword. In AWTWB, Simon is further distanced from magic but reunited with a sword - he reclaims a strength that truly belongs to him, down to his muscle memory. And that sword being the Salisbury Excalibur, a family heirloom, stands in beautifully for the magic that was Simon’s birthright as a mage, that he should have inherited from Lucy. It’s a point of connection to his heritage and the World of Mages.
Simon being immune to magick and incapable of performing magic does set him apart from the World of Mages, but doesn’t remove him from it entirely. For one thing, he’s not the only magick-less mage anymore, and for another he has Shep - someone who also exists on the boundary between the magickal and non-magickal worlds - to help him navigate that liminal space. To tell him that he can put zippers on his shirts instead of spelling them to fit his wings. To maybe even help him meet others with magickal physical traits but little to no actual magic!
So I think Simon’s magickal immunity is a positive thing. I think it’s a physical manifestation of him beginning to move past the abuse and trauma he suffered and learning a new way to move through the world - different and perhaps not without grief, but safer and better able to protect himself. What’s going to bother me forever is the magickal logistics behind why Smith-Richards’ spell had that affect on him. Give me the magic-theory lesson behind that, Rainbow!!