How do we know that it is an extremely important event when Kino went to sell his pearl?

We know that it is an important event because the villagers abandon their regular routine. The canoes remain on the beach, and the villagers await Kino's journey, as they intend to go with him.

The neighbours, watching Kino's door through the crevices in their brush houses, were dressed and ready too. There was no self-consciousness about their joining Kino and Juana to go pearl selling. It was expected, it was an historic moment, they would be crazy if they didn't go. It would be almost a sign of unfriendship.