What did the first Christians believe?
As stated at Jesusneverexisted.com, "The evidence shows clearly that the Christians took over pre-existing beliefs and sacraments rather than introduced new ones." There are many mythologies involving a man/god who is born of a virgin, who is sacrificed in some way and then resurrected. "The earliest Christian theorists denied a physical incarnation of their Lord and knew nothing of the Bethlehem saga." Details of the Jesus myth were added over the decades, the story being passed along sort of like the telephone game children play.
Christians were a relative minority until it aligned itself politically with the State. As for "Biblical accounts" which Christians revere as "divinely inspired", in actuality, they were written by imaginative human beings. Can't deny that the Bible is a collection of some very interesting storytelling, but as I said, invented by human imagination just as any other mythology of the many cultures.
I would call it historical fiction, like a John Jakes novel. Certain historical events strew in here and there and added fiction to spice it up. Most of these tall tales in the Bible are fables, many are based on mythologies of other cultures. Yet many people believe these far-fetched tales to have actually happened, without having evidence. Many of the Biblical characters are fictitious. The existence of the historical Jesus has been an ongoing argument for ages.
There are actually some 200 gospels, epistles and other books concerning the life of Jesus Christ. Writing such material was a popular literary form, particularly in the 2nd century. The pious fantasies competed with Greek romantic fiction. Political considerations in the late 2nd century led to the selection of just four approved gospels and the rejection of others. After three centuries of wrangling 23 other books were accepted by the Church as divinely inspired. The rest were declared 'pious frauds'. In truth, the whole lot belongs to a genre of literary FICTION.
And Christians still cherish their persecution complex, that much hasn't changed.
The first believers in Jesus maintained he was an ethereal spirit, much like other sky/sun-gods. Only later did he acquire a human death, a human life and finally a human birth. The composite 'Jesus Christ' character – god, man, king, carpenter, conqueror, peace-maker, dispenser of justice, advocate of love – was assembled to try and unify a fragmented and fractious messianic religious movement.
In the mid-2nd century the Jewishness of the faith was purged but apologists had little to say about a human Jesus. They took comfort in noting similarities between their own ideas and pagan myths. The Christians remained a minority until well after one particular faction formed a political alliance with the Roman State. The orthodox creed remained unpopular for centuries and persecution was necessary to impose its will.
Christianity is evolving all the time, even now. The Christianity of today is a "touchy-feely" kind of religion, and a belief that this God is some kind of magical genie and Jesus is their best pal who walks and talks with them and is their emotional crutch. The Jesus of today is for the "me" culture, self-centered and softened while all the bad parts of their mythology are ignored (except for the gory zombie Jesus part and the threat of eternal flaming Hell and suffering for non-believers). Thanks to ChuckA for the link to jesusneverexisted.com. Kenneth Humphreys has done a lot of work to put together an interesting site with lots of things to read, consider and discuss. Humphreys even cites his sources.