The document discusses the origins and key characteristics of the Catholic Church. It describes how the Church began on Pentecost when the Holy Spirit descended upon the disciples and they went out to preach. The four main characteristics or "marks" of the Church that are expressed in the Nicene Creed are that it is one, holy, catholic, and apostolic. It provides further explanation of each mark, noting that the Church is one in faith, sacraments, and sacrifice under one head; holy as founded by Jesus Christ; catholic or universal across all ages and nations; and apostolic by continuing the mission of Jesus through the Apostles.