The document discusses the essential marks of the Church - that it is one, holy, catholic, and apostolic. It provides scriptural evidence and teachings from the Catechism to explain each mark. For the Church to be one, Christians must strive for unity through love. The Church is holy as the Holy Spirit guides believers to holiness. It is catholic or universal as Christ calls all people to salvation. And it is apostolic as built upon the foundation of the apostles' teaching.