The Pharisees did not think of themselves as niche interest group, rather, they were propagating and practicing what they believed to simply be the Judean way of life as God required it, as the Torah taught it, and as they understood it. What stood in the way of that was, of course, the contamination of foreign domination, which had to be addressed one way or another, beginning with themselves. Only once they had dealt with the pollution of the self, the village, and the land, would God cleanse them from the contamination of foreign powers. They had an objective and wanted to see the whole nation get on board with it. Wright puts it well: “The Pharisaic agenda remained, at this point, what it had always been: to purify Israel by summoning her to return to the true ancestral traditions; to restore Israel to her independent theocratic status; and to be, as a pressure-group, in the vanguard of such movements by the study and practice of Torah.”
Why the torrid debates with Jesus? Jesus was arguably closer to the Pharisees than to any other Jewish sect and he drew many admirers and adherents from the Pharisees. Jesus and the Pharisees were both very much concerned with the matter of how to see kingdom of God come, which meant they were natural interlocutors (Mk 15:43; Lk 17:20). Some Pharisees, just like Jesus, sought baptism from John the Baptist (Mt 3:7) while others rebuffed it (Lk 7:30). Many Pharisees were impressed with Jesus’s teaching (Jn 3:1-4) and his power to heal (Lk 5:17). They invited him to dinner, which was more than polite hospitality, it meant honorary membership (Lk 7:36; 11:37; 14:1). On one occasion they warned him about Herod Antipas’ pursuit of him (Lk 13:31). A Pharisee apparently helped bury Jesus (Jn 19:39-40). Many Pharisees joined the early church, bringing with them their erstwhile pharisaic baggage about Gentiles and insistence on circumcision of proselytes (Acts 15:5). In the early days of the Jerusalem church, when Peter and John were before the Sanhedrin, a leading Pharisee named Gamaliel cautioned against punishing them, and instead urged a wait and see approach (Acts 5:34-40). Later, when James the brother of Jesus was executed in 62 CE, at the behest of the high priest Ananus, during an interregnum of Roman governors, one Jerusalem faction complained to Agrippa II about the injustice. This group Josephus describes as “considered the fairest-minded, and who were strict concerning the law,” which is a very probable description of the Pharisees (Josephus, Ant. 20.200-1).
Yet, from the Pharisees point of view, Jesus was something of a potential ally turned bitter adversary. His authority was charismatic rather than halakhic, both had similar aims for Israel’s restoration, but they differed very much over what that would look like and how to achieve. Pharisees were in effect saying to Jesus: God appears to be with you, but if so, then, why do you eat with “sinners” (Mk 2:16; Lk 15:2), why don’t you fast as we do (Mk 2:18), why don’t you wash your hands as we do (Mk 7:1-5; Lk 11:38), why are you so lenient about the sabbath (Mk 2:24; Jn 9:16), why are you so strict on divorce (Mk 10:2), and what is the sign of your authority (Mk 8:11-12)? In the mind of many Pharisees, Jesus appears to be a holy man, but his refusal to adopt their package of Torah/tradition meant he was a rogue and a rival. Whatever points of convergence there were between Jesus and the Pharisees, it was overshadowed by an immense chasm evidenced by Jesus’s practice of open-fellowship with sinners which scandalized the Pharisees. Not only that, but Jesus’s disregard for and denunciation of their traditions was a brutal rebuff to the Pharisees’ centre of gravity. In the end, Jesus did not support the Pharisaic project of cultivating purity and piety as the preferred path to national redemption.