In the history of man, cultures have met and interacted. These interactions sometimes are so limited to leave any significant traces while some last so well to leave indelible marks in the sands of time. Interactions may lead to assimilations which allow for a mish mash of the ways of life herein being considered. Occasionally, relations may lead to a total eradication of the other way. So as man lived aforetime and it still occurs till this day. No one drops his traditional set of beliefs so easily while also striving to make more people come his way. Religions have been central to the existence of people as long as we can possibly think of.
Early in the history of the Church, Christianity conquered lands hitherto alien and averse to it. In these lands were people who followed different shades of religions notably a form of paganism or another. The intermingling and interaction of peoples and cultures facilitated by the Pax Romana resulted in the competition and cross fertilization of religions. This resulted in some elements of pagan worship finding their way into the Christian doctrines. The Cross, the trinity, the idea of human sacrifice for the sake of other men, Easter and Christmas festivities to mention a few.
The American Encyclopedia records:
“The belief in the Oneness of God – as a theological movement – began at a very early stage in history, and in fact it preceded the belief in trinity by many decades. Christianity developed from Judaism, and Judaism firmly believes that there is one God.
The path that led from Jerusalem (the home of the first disciples of Christ) to Nicea (where it was decided in 325 CE that Christ was equal to God in essence and eternal nature) can hardly be described as a straight path.
The doctrine of trinity which was affirmed in the fourth century CE bears no resemblance to the original teachings of Christ concerning the nature of God. Au contraire, it is the opposite, a deviation from that teaching. Hence it developed in opposition to the belief in One God… (27/294).”
Will Durant says:
When Christianity conquered Rome, the new religion (i.e., Christianity) was infused with the blood of the old idolatrous religion: the title of archbishop, worship for the great mother, and an innumerable number of lords who gave peace of mind and were like who exist in all places and cannot be detected with the senses. All of this came into Christianity as the blood of the mother comes into her child.
For the layers of pagan influence on the church.