Steinbeck describes how Kino, Juana and Coyotito are dresses in great detail Why?

Juana knew that they would be remembered for this day because it was such a huge event, and she was determined that they be remembered dressed appropriately for the occasion.

For Kino and Juana this was the morning of mornings of their lives, comparable only to the day when the baby had been born. This was to be the day from which all other days would take their arrangement. Thus they would say, "It was two years before we sold the pearl," or, "It was six weeks after we sold the pearl." Juana, considering the matter, threw caution to the winds, and she dressed Coyotito in the clothes she had prepared for his baptism, when there would be money for his baptism. And Juana combed and braided her hair and tied the ends with two little bows of red ribbon, and she put on her marriage skirt and waist.