Barabara G. Walker’s, Man Made God, summarizes a lot of material from other sources. This helps develop an overview of where Christianity came from.
She discusses one of the ancients whose influence continues today, the historian and Bishop, Eusebius. Some of what he wrote continues to be used as important Christian material. But, he was also a participant in some shenanigans.
When the Roman Emperor, Constantine, made Christianity the state religion, he demanded all the gods of that time be made into one. Toward that end, he convened the Council of Nacia where the Bishops of that time made sure that happened. The Trinity and the Nicene Creed resulted.
Who better to bring all this together than Eusebius, a writer and favorite of the Emperor, Constantine. We see him there, not at the time of Jesus, but four hundred years later hammering into place what became today’s Christian faith.
Then, there is the only piece of writing that claims to record the activities of the Jesus preacher “written at the time of Jesus”. This is found in writing attributed to Josephus, a historian recording events at the time Jesus was supposed to have lived.
In the earliest copies of the Josephus writing, there is no account of a Jesus. Then, some 400 years later another historian quotes Josephus writing about a Jesus. The historian who “found” this when others had not (inserted it himself many believe) was the propagandist and promoter of Christianity, Eusebius.
Those of us who don’t believe have our reasons.