Stephen’s last appeal to the hard hearts of the Pharisees…
“Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye.
“Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers:
“Who have received the law by the disposition of angels, and have not kept it.” *
Circumcision was one of the Pharisees' most important laws and ceremonies, so to call them uncircumcised was a huge disgrace. And in their heart and ears?
They also took great pride in the prophets, but they killed each of them that foretold of the Messiah, and then they ended up killing Him too.
The law was their pride and joy, but as Stephen pointed out, in reality, they had not kept it, even though their whole point of being Pharisees was that they were strictly law-keepers.