In addition to this, I remember what the Jewish scholar Nir says about the use of baptism, apparently in contradiction with what GDon has written about a presumed familiarity with the term:
[F]urther incredulity is raised by the presence of βαπτισμός and βάπτισις, the two terms used in the passage for the immersion associated with John. Being quintessentially Christian terms that Christian tradition applied to Christian baptism, they occur in Josephus only within this passage, marking divergence from his usual usage of terms associated with the Jewish ritual of immersion—λούεσθαι, ἀπολούεσθαι, meaning to purify a person from external physical defilement.
https://vridar.org/2013/08/24/so-john-t ... gery-case/
But note that this is not essential to my argument.
While what may help partially the my argument is the Nir's conclusion:
Josephus, as is well known, remained a faithful Jew. He was neither initiated into one of the Jewish-Christian sects, nor did he convert to Christianity. Thus, the inevitable conclusion is that the description of John’s baptism, as provided in the passage under review, was not written by Josephus, but was rather interpolated or adapted by a Christian or Jewish-Christian hand.
(my bold)
Note that Nir is adding further reasons of the
why Josephus had to explain what the baptism was for Josephus.
But even Nir is ignoring the fact that,
even before that Josephus had to give all these informations
in addition about the John's opinions on the baptism (informations that are
surprisingly missing according to Nir), Josephus
had to explain in first place
why a Roman reader should have been interested in such an exotic subject,
when he is deliberately left in the dark about the only fact that could have aroused his curiosity about the John's opinions on the baptism: that he was baptizing a lot of people to the point of being “called Baptist”.
Hence I repeat: only the Christians had the means and right knowledge
to appreciate the explanatory effort attempted by Josephus, who therefore was
not the authentic Josephus, but a
false “Josephus”,
a Christian interpolator.