And the high priest said, “Are these things so?” And Stephen said:
“Brothers and fathers, hear me..."
Stephen's sermon in Acts 7 is a masterwork of historical narrative, theology, and knowledge of God's redemptive work through the centuries of Israel's unfolding story. Stephen really knew the scriptures. His words are a defense against false accusations of blasphemy (Acts 6:11) specifically accusing Stephen of speaking against the Law of Moses and against God. But not once does he talk about himself, just God, Israel, and the Law. False witnesses specifically lie about Stephen speaking against the temple and the Law. They manufacture false charges about him predicting Jesus destroying the temple and changing the Law. He is delivered before the religious council where these false charges are presented.
Stephen then responds to the high priest's question by unpacking the responsibility of the Jews to obey God starting at the call of Abraham. He reiterates a proper understanding of the Abrahamic covenant (the foundation of Jewish theology) placing emphasis upon God's promises and the curses for disobedience, strongly emphasizing how God led Abraham and the patriarchs.
He transitions to the story of Joseph and the Exodus, emphasizing how God kept His promises by raising up Moses. His emphasis by telling the Moses story is on how God's sovereign work over time took a man that the Israelites initially rejected and made him their deliverer. His emphasis through the Exodus story is God's sovereign work, despite Israel's resistance to what God did and who God used.
In the wilderness Israel's rejection of Moses became a rejection of God with the golden calf incident. The result was judgment even as the Law was brand new. Still, God was gracious giving them first a tabernacle to worship in, and later the temple in the Promised Land. Stephen quotes scripture to reiterate that even with localized worship, God was above any temple and wanted Israel to worship Him beyond any "place" of worship, making God the first voice to speak "against" the temple.
Stephen's conclusion, biblically grounded and proven, was that Israel rejected God routinely throughout history, working against God's work at nearly every turn. The received the Law but did not keep it. As revelation about God increased with each new moment in the Israel story, the nation still responded with some rejection of what God revealed. And Stephen's preaching of this truth go him killed, ironically proving his sermon's point in the most dramatic way.