Thanks for that, Ben.
Regarding Josephus' statement in Ant. 18.1.1 that the Fourth Philosophy was a "system of philosophy,
which we were before unacquainted withal" and that "
the customs of our fathers were altered" by it, since Josephus was a Pharisee I take his reference to "the customs of our fathers" as meaning the oral Torah of the Pharisees, given that this is commonly how the oral Torah is described (including in the NT), and it is in keeping with what he says about the Pharisees in Ant. 13.10.6:
What I would now explain is this, that the Pharisees have delivered to the people a great many observances by succession from their fathers, which are not written in the laws of Moses; and for that reason it is that the Sadducees reject them, and say that we are to esteem those observances to be obligatory which are in the written word, but are not to observe what are derived from the tradition of our forefathers.
And this is the same thing that Jesus does in the NT. As Mk. 7:1-13 says:
The Pharisees and some of the teachers of the law who had come from Jerusalem gathered around Jesus and saw some of his disciples eating food with hands that were defiled, that is, unwashed. (The Pharisees and all the Jews do not eat unless they give their hands a ceremonial washing, holding to the tradition of the elders. When they come from the marketplace they do not eat unless they wash. And they observe many other traditions, such as the washing of cups, pitchers and kettles.)
So the Pharisees and teachers of the law asked Jesus, “Why don’t your disciples live according to the tradition of the elders instead of eating their food with defiled hands?”
He replied, “Isaiah was right when he prophesied about you hypocrites; as it is written: “ ‘These people honor me with their lips, but their hearts are far from me. They worship me in vain; their teachings are merely human rules.’ You have let go of the commands of God and are holding on to human traditions.”
And he continued, “You have a fine way of setting aside the commands of God in order to observe your own traditions! For Moses said, ‘Honor your father and mother,’ and, ‘Anyone who curses their father or mother is to be put to death.’ But you say that if anyone declares that what might have been used to help their father or mother is Corban (that is, devoted to God)— then you no longer let them do anything for their father or mother. Thus you nullify the word of God by your tradition that you have handed down. And you do many things like that.”
This is also how I take Paul's statement in Gal. 1:13-14 about his previous life in Judaism, since he says he had been a Pharisee in Php. 3:5.
For you have heard of my previous way of life in Judaism, how intensely I persecuted the church of God and tried to destroy it. I was advancing in Judaism beyond many of my own age among my people and was extremely zealous for the traditions of my fathers.
This alone, in my view, would be enough to explain why the Pharisees are presented as wanting to kill Jesus in the NT, since they regarded the oral Torah as being divine and, as Josephus notes, it was the law of the land at the time (and in most forms of Judaism to this day), to such a degree that Josephus says that even the Sadducees had to go along with it in Ant. 18.1.4:
But they [the Sadducees] are able to do almost nothing of themselves; for when they become magistrates, as they are unwillingly and by force sometimes obliged to be, they addict themselves to the notions of the Pharisees, because the multitude would not otherwise bear them.