Unity as the aim, not the starting point of early Christianity: when one of the Jesus Groups started missionary activity,
this certainly constituted a differentiation from the original movement. I will leave open the question of whether we should speak of a Jesus group, a Jesus fraction or an individual church at this point.
In any case, I am convinced that Christianity did not begin as a united movement, but as different groups or individual churches.
The most important textual confirmation for individual churches is the transfiguration narrative: during the vision on the mountain, Peter says to Jesus (Mark 9:5) “Let us build three temples (skhnh = tent; see also LXX: tabernacle), one for you, one for Moses and one for Elijah”. In other words, Peter points to the three individual churches of Peter, James and John.
However, Mark’s Gospel already stands for the union of the individual churches. That is why he writes: Peter did not know what to say (verse 6). More evidence can be found in Mark 9:38ff, where the account mentions an unknown exorcist. Comparisons may also be drawn with the divisions in the church in Corinth criticised by Paul: 1 Cor. 1:12.
The Jesus Groups finally separated from their original movements only after the end of the Jewish Revolt in 70 AD.