What went on in those early "services?" What was the "ritual?" In Rome? In Jerusalem, or Ephesus? What did the learned, official leaders of the Jews of the time think ... or write ... about Jesus? (although some of these commentaries definitely exist, they don't seem to be much studied. Top Secret?)
In regard to Constantine, he appeared as baffled by these questions as I am. However, once the Council made up its mind, he followed their direction. IMNVHO, it is also a bit naïve to ignore that Constantine's conversion and influence had a lot to do with eventually making Christianity as practiced and defined in Rome and Constantinople the "state religion."
The point being that no one is damned for not knowing the answers to these questions .... or asking them. The Bible is, IMO, of little specific help in answering them ... so tradition must count, too.
How? How much? Whose?
In 50 AD or thereabouts, the Romans believed that Christianity was a sect of Judaism. In fact, for a long while official Rome tended to hold the Jews responsible for any “problems” perceived to be caused by Christians!
The early Christians were called Jews.
With out going into detail it is pretty obvious that the gentiles thought that since they were adopted children they would be expected to keep the same law as the Jews.
That is why Paul had some problem making them understand that they were not saved by the law.
At any rate it is a fact that Christianity was brought to us by Jesus who was a Jew and by the apostles who were also Jews and all of the teachings were also based on the laws of God which were handed down through the Jews.
So how the Jews got put out i have no idea.