I showed previously how Eusebius, the ancient "historian" of the early Church, had to resort to legends and left great lacunae in his story of the rise of Christianity, because the Catholic Church lacked any real records or traditions from the First Century. The New Testament book of Acts of the Apostles and the legends written up by Eusebius combined to produce an entirely legendary picture of the earliest period of the rising religion.
Now let's see how the puzzle-pieces of a new, alternative, critical view of Christianity's first century might fit together. I think the reality looked something like the following outline. Some parts of the story are based on direct evidence, in which case I have linked to books and articles, or explained the evidence myself. Other parts have to be imagined as necessary steps in order for the rest of the story that is in evidence to have taken place. I have put these essential but only circumstantially supported speculations in italics.
Various Jewish strains of Messiah-belief are apparent in Daniel, Zechariah, Philo, and later sources concerning a heavenly Son of God, Logos, End-Times figure, with the name Jesus attached to some versions. Some thinking Jews, in the face of repeated failure to overthrow the Roman occupation by force and repeatedly prey to false military messiahs such as those recorded by Josephus, seek a new interpretation of Messianism whereby the sins of the nation will be cleansed and the defeat of their enemies begun.
See Carrier, On the Historicity of Jesus for these pre-existing background ideas, among many other things.
As an example, the Septuagint (ancient Greek) version of Zechariah 6 discusses "Joshua [i.e. "Jesus" in Greek] the son of Jehozadak [= "Yahweh the righteous"], the high priest" who "shall build the temple of Yahweh; and he shall bear the glory, and shall
sit and rule on his throne; and he shall be a priest on his throne". When Philo discusses this passage, he says of this Jesus figure that he is: "an incorporeal being who in no respect differs from the divine image" and goes on to say: "For the Father of the universe has caused
him to spring up as the eldest son, whom, in another passage, he calls
the firstborn; and he who is thus born, imitating the ways of his father". Thus Philo, an Alexandrian Jew of the same age as the supposedly historical Jesus, already and independently conceived of a heavenly figure named Jesus, a son of God made in the divine image, who would be a ruler and high priest. This proves that the heavenly Jesus had been imagined without any reference to any Jesus of Nazareth, and it disproves the common idea that Jesus must have started as a man and been progressively deified. The actual process was the direct opposite.
Circa 30 (?)
One version of this Jesus-Christ (= "Joshua Messiah") belief coalesces around the "Pillars" Peter, James and John, when they think to decrypt Old Testament prophecies so as to find messages from heaven concerning his descent, crucifixion and resurrection in the heavenly realms. Their essential faith is that Jesus died a sacrificial death, crucified by evil demons in the lower heavens, in propitiation of the justice of God towards the sins of the nation, thereby substituting his ultimate sacrifice for the Jews' feeble efforts to satisfy God through the Temple cult.
Again, see Carrier's new book or start with his essay outlining his arguments for the Jesus Myth theory, on which I collected introductory readings here. Also see his presentation on where Jesus came from, here (pdf). In particular, see the chapter in Carrier's book dealing with the New Testament book called Hebrews, where he shows that this is the theology it preaches: this is probably the original Christianity, Judaism reformed and transformed by the sacrifice of the son of God.
Circa 45-50 (?)
Simon Magus (a.k.a. Simon of Samaria) announces a new understanding of Jesus belief, whereby the old dispensation of the Torah is not divine, but is instead the oppressive creation of intermediary ruling demons who created the Earth and trapped our spirits in material bodies. His essential faith is that through baptism we participate in the death and resurrection of Jesus, thereby freeing us from death and thus from the power of the legislating demon powers who rule the Earth. His creed is based on the "Vision of Isaiah". His movement also produces the original of the Gospel according to Mark as an allegorical expression of their belief and an attack on the Petrine Jewish Christian movement. GMark is written in the form of a historical fiction as a midrash (a form of scriptual pastiche) on the OT prophecies revered by Christians, especially those from the Psalms, Isaiah, and the later prophets. Simon writes the originals of the Pauline epistles, including the letter to the Galatians which cautions his flock against listening to the Jewish Christians who want to impose Jewish cultic requirements on them.
See Hermann Detering's The Fabricated Paul (online) and Roger Parvus' ongoing series of articles on "A Simonian Origin for Christianity" for the theory of the identity of Paul and Simon Magus. See Robert Price's article here or his Incredible Shrinking Son of Man for the scriptural basis of the Gospel stories.
Circa 60-70 (?)
Simon Magus' writings are edited and interpolated by a Proto-Orthodox writer who names him Paul so as to critique Simon and make him appear to promote orthodox belief in the divinity of the Torah. This Proto-Orthodoxy is a new development, combining the belief of the Jewish Christians in the divinity of the Law with the belief of the Simonians in Christians' freedom from the Law. Whereas the Simonians held themselves released from the Law imposed by the demonic world-rulers, and their punishment of death, through participation in Jesus' resurrection which nullified the power of the demons over them, the new Proto-Orthodoxy held that Jesus had taken the punishment of the Law on himself, atoning for human sins, and freeing humanity from the Law through substitutionary fulfillment.
Gnosticism thrives as ideas about Jesus and other heavenly emissaries are mixed and matched with all manner of Jewish, Greek and Egyptian esoterica.
See Parvus' articles for the interpolation of orthodoxy into the Pauline epistles.
Somehow, whether due to the loss of traditions in post-70 Judea, or to its efficiency as a meme, or to its utility to the Proto-Orthodox in establishing their apostolic bona fides, the surface allegory of GMark is spread as if it were a historical report: the belief arises and proliferates that Jesus of Nazareth was the crucified and resurrected Messiah.
There is no definitive evidence of the replacement of the Heavenly Jesus
by the Historical Jesus as the dominant christological belief, although
there are suggestive items in both the NT and in the letters attributed
to Ignatius where orthodox writers seem to criticise and reject others
who deny the reality of the incarnation. It is arguable however whether
it is mythicists or docetists they have in mind. Consider Trallians 9: "Be ye deaf therefore, when any man speaketh to you
apart from Jesus Christ, who was of the race of David,
who was the Son of Mary, who was truly born and ate and
drank, was truly persecuted under Pontius Pilate, was
truly crucified and died in the sight of those in heaven
and those on earth and those under the earth; who moreover was truly raised from the dead." Whether or not this is valid evidence for the thesis, if we accept that the original Jesus was heavenly, and the later Jesus was human, then there must have been a period of change-over, even if the best evidence is lost.
Once the proliferation of the Markan tale occurs, Orthodoxy now comprises a combination of beliefs in a Historical Jesus and in the divinity of the prior Torah dispensation. There is a great loss of documents from the first-century, not preserved by what came to be the Church with a capital C. Therefore, despite its claims to apostolic tradition and historical precedence, when Eusebius much later comes to write the history of the early Church he is virtually unable to find any documentary records. During this period, Matthew is written as a Jewish-Christian revision of GMark, promoting the fulfillment of the Torah, rather than its rejection. The original of GLuke is also written, based on both GMark and GMatthew. What became the Catholic Church has no particular importance among the welter of competing Christianities across the Eastern Mediterranean and Middle Eastern worlds at this point.
Also during this period, Marcion emerges as a critic of Proto-Orthodoxy, claiming that Paul's epistles have been systematically Judaised by the followers of the Petrine group of apostles who failed to understand Jesus' radical anti-Law message. He is the first to collect and publish a book containing both a Gospel and a selection of Pauline letters. Marcion is not able however to get his hands on copies of the Pauline originals; he uses a version of GLuke different from ours. Marcion and some Gnostic groups take the Historical Jesus for granted but reject the God of the Jews as a demonic demiurge who created the material world in order to trap spirits in bodies: they thus reject the fleshly incarnation of Jesus and espouse docetism, the belief that Jesus only appeared to have a fleshly body. (This is a speculation of how docetism arose, fitting it into the general pattern, rather than a process seen in direct evidence.)
See Joseph Tyson's Marcion and Luke-Acts, especially chapter 2 on Marcion, online here. For the welter of competing Christianities in this early period, see Walter Bauer's Orthodoxy and Heresy in Earliest Christianity, online here.
In the face of the rise of Marcion's Church, a Proto-Orthodox writer or writers (Polycarp?) interpolates GLuke with anti-Marcionite passages, and composes Acts to turn Marcion's anti-Petrine Paul into Peter's faithful orthodox colleague. The NT is published, containing Gospels, Acts, the interpolated and forged Paulines, and some new, orthodox Pastoral epistles, along with Revelation. From this edition onwards, decisions about which writings to include are made on grounds of their orthodox character, rather than their historical authenticity. The Proto-Orthodox also claim the writings of the Apellean (a branch of Marcionism) celebrity Peregrinus as those of one of their own, Ignatius of Antioch; the original Gospel of John may be Apellean in character.
See Tyson again on the anti-Marcionite editing of GLuke and composition of Acts. See David Trobisch's The First Edition of the New Testament for the creation of the orthodox New Testament. For the principles actuating the selection of the canon, see Carrier's summary of the formation of the canon.
Proto-Orthodoxy continues its struggle with Marcionism, whose followers are said to be widespread across the Empire. With the conversion of Emperor Constantine in 313, the Catholic Church is able to bring coercive force to bear on its rivals, who are now labelled by the Church's heresiologists as heretics who have distorted the original, apostolic doctrine delivered by Jesus to the Twelve Disciples of the Gospels and the Paul of Acts. In fact, the Catholic Church, having forgotten the original non-historical character of Jesus, and having adopted and manipulated texts produced by its opponents, and having forged others, has no real claim to historical precedence or apostolic tradition.