This most likely represents the Roman Missal. According to Wikipedia, the Roman Missal is "the liturgical book that contains the texts and rubrics for the celebration of the Mass in the Roman Rite of the Catholic Church." It was adopted in the thirteenth century in an attempt by Saint Francis of Assisi to collect and homogenize the variety of prayers and scriptural readings for Mass into one text.

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Church of the Transfiguration in Philadelphia, PA. 2009. Photograph by Matthew Christopher of Abandoned America. If you'd like to learn more about this location, it is a featured chapter in the book "Abandoned America: The Age of Consequences," which you can order signed copies of here. It's also available (unsigned) through Amazon/Barnes & Noble/Powells/Indiebound/Booksamillion. You may also be interested in my new book, Abandoned America: Dismantling the Dream, available on Amazon, Barnes & Noble, and many other online booksellers across the globe.