It is in every sense without a peer among human associations.
The annals of Christianity in its widest sense are occasionally dated from the creation of man, seeing that a Divine revelation was made to him from the beginning.
While the Church remains essentially the same despite the changes which she undergoes in time, these changes help to exhibit more fully her internal and external life.
As to the latter, ecclesiastical history makes known in detail the local and temporal expansion or restriction of the Church in the various countries, and indicates the factors influencing the same (History of Missions, in the widest sense), also the attitude which individual states or political bodies and other religious associations assume towards her (History of Ecclesiastical Polity, of Heresies and their Refutation, and of the Relations of the Church with Non-Catholic Religious Associations).
Thanks to the light of revelation we know that this one true religion is the Christian religion, and, since there are different forms of the Christian religion, that the true religion is in particular the one known as Catholic, concrete and visible in the Catholic Church.
The history of Christianity, therefore, or more properly the history of the Catholic Church, is the most important and edifying part of the history of religion.
We are now in a position to grasp the scope of ecclesiastical history.
As the institution which the Son of God founded for the realization on earth of the Kingdom of God and for the sanctification of man, the Church has a double element, the Divine and the human.
The principal subject of history is man, since the external changes in his life affect closely his intellectual interests.
Objectively speaking, history is the genetical development of the human mind and of human life itself in its various aspects, as it comes before us in series of facts, whether these pertain to individuals, or to the whole human race, or to any of its various groups.
The Divine element comprises all the truths of Faith which her Founder entrusted to her His legislation and the fundamental principles of her organization as an institute destined for the guidance of the faithful, the practice of Divine worship, and the guardianship of all the means by which man receives and sustains his supernatural life (see SACRAMENTS; GRACE).
The human element in the Church appears in the manner in which the Divine element manifests itself with the co-operation of the human free will and under the influence of earthly factors.