Greco-Roman Religions might be considered “the competition” of early Christianity, but this is not a fair description of how religions functioned in the first century.

A Guardian lares

First, in the first century, religion was rarely a choice. A person owed Worship to a god because of a civic or family obligation or because the god is associated with a trade. A person living in the Roman world would not even think in terms of “converting” from one god to another, since gods had various functions; motivations were purely practical.  If one was going to sea, one appeased sea gods. In fact, the idea of choosing to worship a particular god was the attraction of the mystery cult. One might become a worshiper of Mithras by choice, although obligated to also worship other gods.

“The family cult was also the natural point of departure for the veneration of the dead…