I had this pitch for a campaign once: long ago, the world was ruled by two powerful empires, a Theocracy and a Magocracy. The two clashed in a terrible, unspeakable war. Continents were reshaped, and many strange and bizarre creatures were birthed into the world.
In the end, the High Priests asked their Gods for succor, and the response was the Thaumaturgic Cessation. A wave of power drained much of the magic from the world- monsters became ordinary beasts, and all the races of the world lost their magic.
Over the centuries since, magic has returned to the world, and the people have learned a hard lesson about how it is to be used responsibly. While exploring a ruin, a learned academic discovered a cache of ancient, well-preserved scrolls intended as a primer of sorts, for apprentice wizards.
He founded an organization that has two purposes- to accumulate arcane lore, and train a new generation of wizards, all of whom take an oath to use their powers for the betterment of the world.
You are one of these fledgling magicians, sent out into the world with a meager amount of spells at your disposal, to seek out and share with the Society lost magics. You can either return to the Society to gain new spells, from the limited pool available to them (after making sure your dues are up to date), and trade whatever magical items or spells you have found for rewards/services- or you must find scrolls and spellbooks in forgotten and forbidden places, facing unknown dangers, as the magical beasts and creatures of old have awakened and regained their powers...