Stephen calls the religious leaders of his day stiff-necked and uncircumcised because their hearts resist the Holy Spirit. In his boldness, he accuses their fathers of persecuting the prophets and now killing Jesus who is known as the Just One. To top it all off, they requested the release of a murderer and the blood of Christ is on their hands, which also makes them murderers!
When someone preaches with that kind of boldness and hits a nerve, there can only be two choices in how to react to it. We either accept our part and bow our hearts in repentance, or our hearts are filled with rebellion and resistance. "When the members of the Sanhedrin heard this, they were furious and gnashed their teeth at him." This is what a lack of repentance can do to a person. We see this kind of resistance all over the world.
To top it all off, Stephen is given a wonderful vision of an open Heaven and Jesus standing at the right hand of God. When he relates what he saw. This declaration is what brought about the stoning death of Stephen. It is at his death that we are introduced to the young man Saul who will later become the Apostle Paul. It is no secret what God can do. But it takes a broken will and a humble spirit to allow Him to do for us what we cannot do for ourselves.