Why were the Jewish leaders so upset with Stephen who did wondrous miracles?

Answer 1

The Jewish leaders could not bear the message Stephen brought and the challenges he set before them. He exposed their sin and their resistence to the work of the Holy Spirit. Stephen also saw a vision of Heaven, and this enraged th Jews even more since Jesus whom they could not accept as Messiah was together with God.

Here's what Stephen said which angered the Jews so much (Acts 7):

51Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye.

52Which 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:

53Who have received the law by the disposition of angels, and have not kept it.

54When they heard these things, they were cut to the heart, and they gnashed on him with their teeth.

55But he, being full of the Holy Ghost, looked up stedfastly into heaven, and saw the glory of God, and Jesus standing on the right hand of God,

56And said, Behold, I see the heavens opened, and the Son of man standing on the right hand of God.

57Then they cried out with a loud voice, and stopped their ears, and ran upon him with one accord,

Answer 2

Nothing is known about Stephen outside the Acts of the Apostles, leaving open the possibility that Stephen was a literary creation if the author of Acts did not want to write one of the twelve disciples out of his story at this early point.

While he was being tried by the Jewish leaders, Stephen made no attempt to defend himself, or even talk about his Christian faith as later martyrs are said to have done. He merely began an elementary lecture on Jewish history, a speech so totally irrelevant to Stephen's predicament that it could only have been written by the author of Acts to set the scene for what was about to occur. While Stephen was thus lecturing the Jews in his own defence, he looked up and saw the heavens open and Jesus standing on the right hand of God. Stephen told the Jews what he alone could see, at which they cast him out of the city and stoned him.

Answer 3

The ancient history of Judaism is replete with miracles which were done before the eyes of the entire people. Had there been any such convincing display in the era which your Question refers to, then Jewish law would require them to accept Jesus (or Stephen, etc.) as one of the Prophets. According to Jewish tradition, that did not happen. See also:

Why didn't they accept Jesus?