Christian Church is a term used by some to refer to the whole group of people belonging to the Christian religious tradition throughout history. The term Christian Church, in the first understanding, which is generally used by Protestants, does not refer to a particular denomination.
However, the majority of Christians belong to groups that consider themselves to be the one true church, to which other Christians do not belong. The three largest such groups are the Catholic Church, the Eastern Orthodox Church, and the Oriental Orthodox communion.
On February 27, 380, the Roman Empire officially adopted the Trinitarian version of Christianity as the state church of the Roman Empire. Prior to this date, Constantius II (337-361) and Valens (364-378) had personally favored Arian or Semi-Arian forms of Christianity, but Valens’ successor Theodosius I supported the Trinitarian doctrine as expounded in the Nicene Creed from the 1st Council of Nicea.
Also on this date, Theodosius I decreed that only the followers of Trinitarian Christianity were entitled to be referred to as Catholic Christians, while all others were to be considered to be heretics, which was considered illegal.
In 385, this new legal situation resulted, in the first case of many to come, in the capital punishment of a heretic, namely Priscillian, condemned to death, with several of his followers, by a civil tribunal for the crime of magic.
In the centuries of state-sponsored Christianity that followed, pagans and “heretical” Christians were routinely persecuted by the Empire and the many kingdoms and countries that later occupied the place of the Empire, but some Germanic tribes remained Arian well into the Middle Ages.
During its early history, Christianity grew from a 1st-century Jewish following to a religion that existed across the entire Greco-Roman world and beyond. The first Christians were essentially all ethnically Jewish or Jewish Proselytes.
In other words, Jesus preached to the Jewish people and called from them his first disciples see for example Matthew 10. However, the Great Commission is specifically directed at “all nations,” and an early difficulty arose concerning the matter of Gentile (non-Jewish) converts as to whether they had to “become Jewish” (usually referring to circumcision and adherence to dietary law), as part of becoming Christian.
Circumcision in particular was considered repulsive by Greeks and Hellenists while circumcision advocates were labelled Judaisers. In spite of these at-times intense persecutions, the Christian religion continued its spread throughout the Mediterranean Basin.
There is no agreement on an explanation of how Christianity managed to spread as successfully prior to the Edict of Milan and the establishment of Christianity as the state religion of the Roman Empire. For some Christians, the success was simply the natural consequence of the truth of the religion and the hand of Providence. However, similar explanations can be claimed for the spread of Islam and Buddhism.
Christianity developed out of Judaism in the 1st century C.E. It is founded on the life, teachings, death, and resurrection of Jesus Christ, and those who follow him are called “Christians.” Christianity has many different branches and forms with accompanying variety in beliefs and practices.