Potentially an amalgamation of Ayleid and Aldmer beliefs.
Or, and this is radical, let's talk about Magnus being the third side of the space-time coin.
Well, then it wouldn't be a coin, but...anyways
I always felt that Magnus was on par with DA BIG A and DA BIG S.
Aka-time, Shez-space, Mag-______
Now we must fill in the blank.
Thought? Crafting (in the sense of the concept of creation)?
EDIT: By Vehk I got it! Light. Magnus is light! Now, you might be thinking "Alk, no [VEHK]ing duh", but let's think of the ramifications of it. Light is the source of all life, and creates division (light and darkness). Light also is a substance that exists as both a particle and wave simultaneously.
If Auriel is the soul of Anuiel soul of Anu, and Lorkhan is the soul of Sithis soul of Padhome, Magnus is the soul of Mundus soul of the
Aurbis itself. He is what makes a difference between A and S; their [M]ediator, if you will.
But then Shezzar/Lorkhan stole the place as "soul of Nirn". I smell an enatiomorph!
...or I could just be grasping at straws.