What is a short summary of the story, The Mass of St. Sylvestre, from the collection, The Woman Who Had Two Navels?

The Mass of St. Sylvestre shares a traditional story of St. Sylvestre's feast and first mass of the New Year. The divine event is not open to mortals, but anyone who is able to attend will celebrate the next one thousand new years. Mateo the Maestro, a local magus obsessed with mortality, connives a way to find out if this legend is true, and ultimately pays the price.