The Nature of Magic

Magic in the Game
Is there an explanation for magic? I was watching a YouTube vid by Corey Morine (https://www.youtube.com/watch?v=qiPaYoq_UFw) and he mentions an old handout he made up to explain how magic works. I took it that he wasn't talking about game mechanics, after all, that's in the book. No, I think he is talking about explaining the theory of magic in his setting. It got me to thinking and this post is the result.
White Box is pretty vague on just how magic works, or maybe it is clearer to say, why magic works. It just does. A cleric prays for spells and is granted a number each day which are cast through utterances and presenting the "holy symbol". It isn't stated, but often assumed, that a devine being is involved. A magic user studies a spell book, commits a number of spells to memory so they can quickly be cast with a few verbal utterances and somatic gestures. If we follow the logic into the Advanced game, there is a small material component as well. If the source of such magic is known, it remains unstated.
Other games make more effort to define the theory of magic behind their rules. Looking at SPI's DragonQuest game, it states the basis for the ten schools of magic can be found in myth, legend and literature. In other words, DragonQuest (Chivalry & Sorcery and Fantasy Wargaming) derives their ideas about magic from research and therefore presents more than one type of magic.
If one includes literature as a source, the types or theoretical origins of magic seem almost limitless. Perhaps the simplest form is it comes from pacts with demons, devils, elementals or other supernatural beings and such pacts give the magic user the opportunity to cast a number of spells that day.
A more naturalistic explanation of magic might be that it is everywhere and the magic user has a special ability to focus the energy and shape it. Warhammer Fantasy Role-Play calls this "the winds of magic". Some areas may have stronger magic energy than others. The world may have magic bands, called ley lines in some sources. Magic involves shaping forces of chaos in Lamentations of the Flame Princess and Dungeon Crawl Classics RPG. Fey magic in Adventures in Fantasy is song magic.
Where magic comes from and how the user of magic masters his art can be left open to interpretation or can form a major theme in the setting. I like the way White Box handles it (or doesn't) leaving it up to the referee, who again may say very little about the nature of magic, thereby leaving it up to the individual players. Personally, I rather prefer this latter method as it encourages each player to use their own imagination. For me that is always the goal, engage the imagination.