How did Christianity evolve?

A bunch of Greco-Romans got hold of the LXX, read its "philosophy,' liked it and wanted to join the cult.

They read Aristeas, and got an overview of the cultic praxis.

They read Philo, and understood from Philo that the original owners of the text did not deserve to own the text, and that they could adopt themselves into the family line and become its heirs.  They decided they were much more deserving of inheriting the text than its original owners.

The bar Cochba revolt produced texts whose purpose was to incorporate the brief, unimaginable victory over the Romans, and the savior who accomplished it into the Judean canon.  When the revolt failed, Greco-Romans took it as one more sign that the original owners of the text did not deserve to own it, and read the narratives of its hero as biographies of the saviour they had been "promised."

After the Judeans were expelled from Jerusalem and Judean, Justin Martyr wrote his complaint to Hadrian's successor, conflating all of the above into a single narrative.

Thus was born the "church."

The Judeans, having nearly been annihilated by Greco-Romans, did not want to provoke a further, possibly finishing assault, did not bother to dispute the matter.  They closed off society and began a new canon, organized in a way that would prevent outsiders from accessing and using information.

Built into the new cult the things we are coming to believe are wrong:  anti-Semitism, anti-Africanism, homophobia, a construction which not only makes women a second sex, but stratifies them into virgin or whore.  Those were not necessarily characteristics of Greco-Roman society.  They were, however, what Greco-Romans believed acceptable, according to their (mis) reading of Philo.