Okay that's what I am confused about, since I thought Immunity To Normal Weapons and treating Immunity like Hardened Armor were two effects of the same power. So as I read it, if an Awakend character were to use a spell on the spirit, then only the Hardened Armor part would apply, meanwhile mundane weapons are nullified due to the Immunity To Normal Weapons part. Then add on top of that the use of word "immunity", which as you mentioned, is a poor way of explaining it. But unfortunately this now sounds more like RAI instead of RAW.
Doom, the RAW is that Immunity grants Hardened Armor equal to Magic *2, as previously stated by several posters. Immunity to Normal Weapons (ItNW) is a
specific form of Immunity (same power, specific application) that applies the Immunity power to any and all natural weapons, as I explain in
my original post.
Immunity to Normal Weapons does nothing to magical attacks. A creature with ItNW gets nothing against a spell (from ItNW, anyways), direct or otherwise (note ItNW say "spells", not "direct spells", so fireball is not subject to ItNW).
It's not RAI, it's the definition of Immunity as specifically stated on page 295. As Gun Nut pointed out, this name is a hold-over from previous editions. Don't try to infer that when they say "immunity", they mean invulnerability, use the definition they provide for the Immunity power. If you do that, you'll be fine.