Acts 7:52

“Which of the prophets did not your fathers persecute? And they killed those who showed before of the coming of the Righteous One, of whom you have now become betrayers and murderers,”

Now Stephen gets to the heart of the matter. Their fathers had revealed what was in their uncircumcised hearts by persecuting the prophets. Indeed, they had bared their hearts by even killing some who had proclaimed beforehand the coming of the Righteous One (Isaiah who according to their tradition was sawn in half in the reign of Mansseh, was probably especially in mind). They had revealed that they had not wanted the Righteous One to come if He was as the prophets had said. And now they themselves had gone even further and had betrayed and murdered the Righteous One Himself. They were all of a piece. It must be seen as quite possible at this point that Stephen in his faith and enthusiasm still hoped that they would repent if he pressed them hard enough.

Apart from the last all these accusations had been made against the people of Israel before by their own teachers (2 Chronicles 36:15; Nehemiah 9:26; Jeremiah 2:30) and by Jesus Himself (Matthew 23:29; Matthew 23:37; Luke 11:47; Luke 13:34; Mark 12:1). As for the killing of the Righteous One Himself Peter had previously made that very clear (Acts 2:23; Acts 3:14; Acts 5:28). The charges were not new. They simply rankled.