The most telling moment in Julia Bullock’s recital on Saturday evening at the Metropolitan Museum of Art came before she’d sung a note. You would expect a musician to bathe in at least a little bit of entrance applause at this, the opening event of one of her most prominent New York showcases to date. But with the lights still up in the auditorium, Ms. Bullock modestly entered with the nine string players. The music began without her swanning on solo — in fact, without any clapping at all. Ms. Bullock seemed to be emphasizing that, at the Met, she would truly be an artist, not a diva, in residence. It’s not that she’s a reticent singer, but she exudes humility. She serves the work she’s singing, even as she makes it better.