She is said to have taught the first spellcaster of the Realms, and to have enabled many of the races to use magic. She is most venerated by wizards and those who use magic or magical items in their daily use. Mystra is the goddess of the essential force that makes all spellcasting possible.
Mystra provides for and tends to the Weave, of which she is effectively the embodiment. The Weave is the conduit that enables mortal spell casters and magical crafters to safely access the raw force that is magic. She supposedly weighs and judges each new spell or magical item to determine whether it should be permitted into the Realms. Although she favors the ethos of good, she has learned that as deity of magic, she must preserve the Balance. While she can prevent the creation of new spells and magic items that her philosophy opposes, she rarely exercises this ability unless they threaten the Weave or magic in general.
I am Mystra. I am the Lady of Might and the Mistress of Magic! I am Power Incarnate! Wherever magic is worked, there am I – from the cold poles of Eceledus to its hottest jungles, whatever the hand or claw or will that works the sorcery! Behold me and fear me! Yet behold me and love me–as all who deal with me in honesty do. This world is my domain. I am magic, mightiest among all those men worship. I am the One True Spell at the heart of all spells. There is no other.
Mystra was said to be a manifestation of the Cosmic Balance—maintaining order in the world of magic by correcting great inequalities if things went askew. Indeed, during The Cataclysm , one of her first acts as the Lady of Spells was to ban the use of all magic greater than ninth level. Among sages and historians this was known as Mystra's Ban. She was not as concerned with the ethics of Good versus Evil as long as the laws of magic were upheld.
Arcana, Magic, Spells