THE QUESTION: why did they separate Jesus from Christ?
hypothesis 1: it was a necessary step of the process of incarnation of a Jesus Christ originally pure spirit, even if descendend on the earth (for example, the priority of the Gospel of Marcion over all the other Gospels). Since a spirit was considered ''naked'' in the Antiquity when he appears without a body, a material body had to be given to the angelic Jesus as his mere recipient, and hence the separation between Jesus and Christ.
The problem with this view: to prove that Mcn preceded Mark is surely difficult. I am interested to the relation between the two Gospels, but I am a bit skeptical about a solution.
hypothesis 2: a ''character confusion'' happened between the god Jesus and the man Jesus, after the 70 CE (or in the 2 CE). The god Jesus was confused, especially in the eyes of Pagans, with a man Jesus crucified by sediction or sourcery.
The evidence of this is in the Barabbas episode, Celsus, Tacitus (if authentic in his reference to Christ and Chrestiani), and in particular Minucius Felix.
This is partially a view shared by Ben in his important A mythicohistorical (hybrid) approach to Christian origins. Maybe the only difference is that he sees a particular man Jesus reflected in the Gospels and confused (deliberately) with Jesus Christ, while I see more particular men named Jesus confused (maybe not even deliberately) with Jesus Christ. The difference is also about who started the confusion:
1) if they were Christians, then they were believing that the news about Bar-Kokhba (or other military messianists) were the news of the Parousia of the victorious Christ. (there is clear evidence that the same author of the Revelation of Peter assumed that Bar-Kokhba was the Christian Christ).
2) if they were Pagans, then that ''character confusion'' is described very well by Kurt L. Noll:
(K. L. Noll, Investigating Earliest Christianity without Jesus, in 'Is This Not the Carpenter?', edited by Thompson, Verenna, 2012, p. 252, note 62, my bold).I suggest that the Jerusalem pillars preached a Jesus who claimed to be a son of David and expected to wage holy war on behalf of the Jewish god in the near eschatological future (in other words, a Davidic messiah similar to those in ps. 2, the Qumran texts or Psalms of Solomon). The proclamation of the cross fits very nicely with this hypothetical 'Gospel according to the Jerusalem Pillars', for any Roman governor would have viewed this type of Jesus as a foolish but potentially dangerous criminal, and the pillars would have used the story of the resurrection to affirm how wrong that Roman governor had been (1 Cor 1:20-25).
As reaction to this unwanted and unexpected ''character confusion'' (was Jesus Christ only a crucified criminal?) by Pagans, some Christians opted for an apology more moderate and apparently more ''rational'' than the simple fanatic exaltation of the divine wisdom against the fallacious ''wisdom of the world''.
This apology was clearly embarrassed by the mention of the name 'Jesus', too much allusive to the concept of Holy War given his diffusion among Jewish messianists (see Jesus son of Saphat in Josephus).
For example, Minucius Felix never mentions 'Jesus', but only 'Christ':
http://www.newadvent.org/fathers/0410.htmFor in that you attribute to our religion the worship of a criminal and his cross, you wander far from the neighbourhood of the truth, in thinking either that a criminal deserved, or that an earthly being was able, to be believed God. Miserable indeed is that man whose whole hope is dependent on mortal man, for all his help is put an end to with the extinction of the man.
But other Christians were more radical than Minucius Felix: Jesus was a mere man, therefore the accusations and the defamations (that continued against him even in their time) were part and parcel of his real passion on the cross, while the true Christ ''remained impassible''. The divine wisdow is still superior to the ''wisdow of this world'', but at that point it was became gnosis.
The problem with this view: This view is assuming simply that the first euhemerizers of the god Jesus were, despite them, the same Pagans by their defamatory and denigrating rumors about the presumed ''true'' belief of the Christians. But Richard Carrier doesn't credit this theory of any confidence.