Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
To the table or to bed
You must come when you are bid.
Not only is this a Mexican proverb, it's a command to the domestic parts of the house—the kitchen and the bedroom. For our girls/women readers, it may be hard to imagine your male friends, partner, uncle, or any old geezer commanding you to do something. But back in the day, women had to listen to the men. Heck, back in the day women couldn't vote. Or drive. Or live in their own apartment.
Tita, however, may be an exception. She's not exactly bid to the kitchen, she's born in it. Plus, she likes it. And, she's never bid to the bed—she's taken there by Pedro (she wants him as much as he wants her). Even so, she, and all the women in Like Water for Chocolate, live in a violent and male-dominated world.