This page, titled "Domica Prima Adventus" (a shortened version of "Dominica Prima Adventus", which translates to First Sunday of Advent or First Advent Sunday). This book would have been used by the choir in a Catholic Church to mark the first day of the liturgical year. Liturgical manuscripts were generally very large, as they were designed to be read from a distance by a choir. This book is 45cm tall (17.7 inches).
The full book is titled "Graduale R.N", and is believed to have been produced around 1750. It has is entirely handwritten, with decorated capital letters at the start of a section, like the letter A on this page. These decorated initials are referred to as "illuminated initials".