As part of historical science, the history of Christianity is a systematic presentation, connection and sequence of the development of Christianity. The subject of Christian history is the subject of monitoring the development and life of a religious community that arose in apostolic times and consists of people united by faith, later defined and expressed in the Creed. Therefore, the subject of history is the social element of Christianity, subject to changes that have occurred throughout history. However, everything Divine, that is, theological, which constitutes the essence and foundation of the Church, such as dogmas and doctrines, the Holy Mysteries and others, being eternal and unchangeable, does not belong to history itself, although, becoming the subject of diverse human understanding of the history of Christianity and the church itself, it also becomes the subject of historical study. The aspects from which Christianity should be viewed as the subject of historical science are indicated by its life itself.

The Serbian Historical Society for the History of Christianity deals with the history of Christianity as a whole from its inception to the Great Schism of 1054, and then only with the history of Orthodoxy, given that the Serbian people belong to the Orthodox Church, and a special part of its work is focused on the study and promotion of the history of Orthodox Christianity in the Balkans and among the Slavic peoples.

The development of Christianity manifests itself from two sides – external and internal. So, we see how Christianity spreads and stands at different times in certain relations to other human societies. This is the external side. On the other hand, we see how the Christian Church takes care of preserving and clarifying its teachings, although in doing so it encounters obstacles from some of its members who deviate from the prevailing teachings and create heresies and schisms, and how it performs the sacred mysteries and divine services. It is governed by a hierarchy and, ultimately, strives to achieve the main goal of its existence – the moral perfection and salvation of its members. All this makes up the inner side of the life of Christianity and the Church.

The history of Christianity as a scientific discipline must be a harmonious overview of the development of all aspects of this subject. Therefore, it is necessary that each aspect of Christian church life be presented in order and chronological sequence. However, since there is a close historical connection between all aspects of Christian church life, it is impossible to examine each of them separately throughout history. On the other hand, examining all aspects of Christian life together in each century is also inconvenient, since there are events that begin in one century and continue in another, and even in a third. By limiting the study of church history to the rigid chronological framework of any given century, we risk losing the coherence of the presentation.