Heart of the Weave
Almost all mortal religions regocnise the excistence of Mystra, Mother of All Magic, but those that have truly devoted to her, also know her Exarchs that serve her purpose, and the purpose of The Weave.
Mythology & Lore
Reverence for Mystra or The Weave exists in some form in most cultures, where the Mother of all-magic is worshipped if not as goddess with her own personality, then atleast as a concept of the flowing, magical Weave. Those who devote themselves to the worship of the Weave's Heart, consider her as the creation of the two mother goddesses, Selune, the light, and Shar, the darkness. Mystra with her essence would become the way for mortals to connect with magic, and possibly even reach divinity.
In this enterpertation, once mortal great wizards that have brought forth exceptional knowledge and feats of magic have been lifted up to become Mystra's exarchs and gods on her side, sharing her divinity. Most powerful of them is Azuth, protector of mages, great patron of abjuration, evocation, conjuration and transmutation magics. He is often worshipped openly with Savras, patron of divination magic. Azuth is also in some interpertations seen as Mystra's consort.
The last two wizards to be held up as Mystra's exarchs are Melif, lord of necromancy and Leira, lady of illusions and enchantments, but both of them are seen a bit more darker entities, and they are more seen as questionable saints than actual gods.
Some do believe whole heartedly, that one that can impress Mystra with their skill, could once get a chance to become a patron deity of chosen magical school, and surpase her chosen.