Two of the Council's sixteen documents—the Dogmatic Constitution on the Church, Lumen Gentium, and the Pastoral Constitution on the Church in the Modern World, Gaudium et Spes—explain the Church's self-understanding of what she is and what she does better than has ever been done in any of the Church's official documents in the course of her long history.

The diversity inherent in the Church as Catholic, or universal, is also covered in the book in a discussion of the Council's Decree on the Catholic Eastern Churches, Orientalium Ecclesiarum. Such currently widely discussed and debated contemporary issues as the primacy of the pope, the collegiality of the bishops, the universal call to holiness, the place of the Blessed Virgin Mary in the economy of salvation, the relations of the Church and Catholics with other Christians and with the modern world, and the dignity of the human person—all of these issues, and how they apply today in the life of the Church, go back to Vatican II and to the Council's great documents on the Church, which are more relevant than ever today with the passage of time.