Bhaisajyaguru is defined by a set of undertakings rather than by a biography. The sutra devoted to him has the Buddha describe an eastern buddha-field and the twelve great vows its buddha made while he was still a bodhisattva, and the vows are unusually concrete. He undertakes that his own body will blaze so that beings may see by it; that those with deformed or incomplete bodies will be made whole; that the sick who have no medicine, no doctor, no family and no means will be relieved on hearing his name; that the hungry will be fed before being given the teaching; and that those bound and punished unjustly will be freed. One vow, that women who wish it will not be born again as women, belongs plainly to the assumptions of its period, and later commentators handle it in a variety of ways.
The emphasis on hearing the name is what made the sutra practical. It supplied a devotion that could be performed by the sick and by those caring for them, with a text to recite, a name to repeat and a set of promises addressed to exactly the situation the reciter was in. That is why the sutra was translated into Chinese repeatedly from the fourth century onward, was copied in enormous numbers, and became one of the standard texts read at sickbeds and funerals across East Asia.