Some Blue posts about Diablo 3 lore issues, regarding Tyrael and other angelic stuff.
Nevalistis: Tyrael’s mortality has no bearing on his ability to wield El’druin. After all, it’s his sword. =) This is also not the first time a mortal being has wielded El’druin. Jacob Staalek once used the sword to great effect protecting his home. This event was covered in the comic books and referenced in the Book of Tyrael.
I still can’t fathom why Malthael wouldn’t try to simply kill Tyrael on the spot, though…
Nevalistis: Malthael is extremely in tune with souls.When he inspected Tyrael’s soul, he found no evidence of demonic taint. Ergo, he did not consider Tyrael his enemy. It really is that simple, as Death tends to see things in black and white.
Nevalistis: El’druin is a unique item in that it isn’t simply an angelic weapon, but a part of Tyrael. In order for Tyrael to be whole again after he cast himself from the High Heavens, El’druin needed to be restored. It’s inexorably tied to his being, regardless of what state Tyrael is in. Hypothetically speaking, if Tyrael were to somehow become an actual human, El’druin would remain equally integral to his being.
I was reading the Book of Cain this weekend and it makes clear that the Angels don’t really have physical bodies; they’re not like, immortal people in shiny armor. Their armor is part of their essence; not something they put on or take off, or send out to be polished by their squires. Witness how Tyrael ripped off his armor when he became human in the cinematic; it was like he was tearing away part of his body, and his shoulder pads just dissolved into nothing once they hit the ground.
The weapons used by the Angels don’t seem to be quite the same. They are weapons; external objects that aren’t just grown out from the Angel’s non-body, but they are also closely attuned to the Angels. Tyrael’s sword as Blue’d above, but also something like Imperius’ spear Solarion. Yes, it’s a stick with a metal point, but Imperius doesn’t carry it around all the time; he can sort of dispel it to nothing when he’s not using it, and when he wants it back he can summon it to his hand like a bolt of lightning from the sky. You see that summoning in the Diablo 3 cinematic before Act Four, and you also see it get broken then by Diablo, and yet it’s whole again later in the act when Imperius is threatening your hero while brandishing it.
It’s not clear how Malthael’s scythes fit into this dynamic; they’re not mentioned or named at all in the Book of Cain, so presumably they’re special as his trademark weapon, but not so character-specific and essential as Tyrael’s sword or Imperius’ spear.