The document discusses the nature of the Church as a mystery. It says that the Church derives its mystery from its Trinitarian origin and manifests the Trinity through its nature and mission. The Church is a mystery because its nature can never be fully understood through human reason alone, as it is a reality that is always greater than what we can comprehend. The Church holds together apparent 'opposites' like being both divine and human, visible and invisible. Through history we can see God's hidden hand in preserving the Church despite difficulties and persecutions.

1. NATURE OF THE CHURCH: AS A MYSTERY

4. Why the Church is a Mystery?

15. The Mystery of the Church as Witnessed in History