From the beginning the Jewish people held the Jesus Movement in high esteem. Although many didn’t fully embrace the Gospel, the Apostles and early believers were not only regarded as harmless to the Jewish faith, but what they preached was part of that faith, just as the sects of the Pharisees, Sadducees and Essenes were so held.
What happened? All of a sudden popular opinion swung to the other end of the pendulum. While the Apostles were still regarded as basically harmless (Acts 8:1), the Hellenist Messianics were not. Moreover, these latter Jews were not only persecuted to the death (Acts 22:4) in Jerusalem and Judea, they were pursued even to foreign lands (Acts 9:1-2; cp. Acts 26:11) to be arrested and brought back to Jerusalem for trial and punishment. In short, Saul, who spearheaded the will of the high priest, made it his personal business to seek out and destroy the early church, if not the whole body of believers (viz. Acts 8:1), certainly those represented by the blasphemous Stephen (Acts 6:8-14).
In Acts 9:1 we are told that Saul was yet “breathing out threats and murder against the disciples of the Lord.” Saul was a zealous man. He was zealous for the traditions of the elders (Galatians 1:14), which led to his wrath against Messianic Jews (Philippians 3:6). In Saul’s eyes his own actions were justified in that he believed his anger (Psalm 27:12) was inspired by divine retribution (Psalm 18:15) and extermination was the will of the Lord (Joshua 10:40).
Saul’s zeal for God was founded, not in God himself, but, in the “traditions of the elders” (Galatians 1:14). Later, Paul confessed his zeal for God was exactly like that of those who wished to kill him (Acts 22:3), which he testifies was expressed in ignorance of the truth (Romans 10:2). The implication, therefore, is that the “traditions of the elders” from which Paul and, presumably, the people who desired to kill him derived their zeal was from traditions of men and not from God at all. Saul’s wrath was, therefore, human and cruel (Psalm 27:12) and not divine justice (Psalm 18:15).
So, what was the presumed blasphemy of Stephen and, by implication, the blasphemy of the Hellenistic Messianic believers? What was it that got the Jews so riled up and ready to destroy what was previously considered a genuine sect of the Jewish faith? From the beginning, in the days when God freed Israel from slavery in Egypt, God told his people that there would be one law in his nation for him who was born in the land and for the stranger (Exodus 12:49). The house of God was to be a house of prayer for all people (Isaiah 56:7). Yet, those born in foreign lands were never really accepted in Israel as true worshipers of God and could not worship with Jews (Isaiah 56:3), because the watchmen were corrupt and blind to what was good (Isaiah 56:9-12). Stephen, knowing the injustice of the present system, repeated what was said in the prophets, namely, that the Lord dwells not in houses made with (human) hands (Acts 7:48), for heaven is the Lord’s throne and the earth is his footstool. Stephen was quoting from Isaiah 66:1-2. This was a prophecy of judgment and condemnation against Israel’s leaders! This is why the whole Sanhedrin rose up in anger against Stephen (Acts 7:53-54), because he was revealing their sins. They, like their fathers, rejected the truth and rebelled against God, even to the point of betraying and murdering the promised Messiah (Acts 7:51-52)!
The context of Isaiah 66 is that the rulers were corrupt. The offerings they made upon the Altar of God was as though they offered abominations (Isaiah 66:3), but their abominations shall make them desolate (Isaiah 66:4, 15-18, 23; cp. Matthew 24:2, 15, 27-30). Most of the rest of Isaiah 66 concerns the joy of the elect for their faithfulness (Isaiah 66:5) and the service of the gentiles in helping Israel (Isaiah 66:19-20), and God will make some of them—i.e. some of those gentiles serving him—he will make some of them Levites and priests to God (Isaiah 66:21).
This is what Stephen showed the Sanhedrin that day, and this is what Saul heard and found contemptible. The gentiles were unclean and could not approach God as they are. Such a thing blurs the clean and the unclean. It was perceived as taking away the service of the Jewish people, making their history irrelevant. Such a doctrine, such a sect had to be destroyed. It was this to which Saul had devoted his zeal gathered from the “traditions” of men (Galatians 1:14), and it was this that recoiled the Jewish people who then refused to listen to Paul as he made his defense before them years later (Acts 22:21-22).