Since by definition a prophet (in Hebrew, na?î) is someone who speaks for God, Stephen became a prophet the very moment he brought God’s rî? against Israel. His prophetic ministry, however, was rather short.
Read Acts 7:55-56. What was the meaning of Stephen’s vision?
“When Stephen reached this point, there was a tumult among the people. When he connected Christ with the prophecies and spoke as he did of the temple, the priest, pretending to be horror-stricken, rent his robe. To Stephen this act was a signal that his voice would soon be silenced forever. He saw the resistance that met his words and knew that he was giving his last testimony. Although in the midst of his sermon, he abruptly concluded it.”—Ellen G. White, The Acts of the Apostles, p. 100.
While Stephen stood before the Jewish leaders discharging God’s case against them, Jesus was standing in the heavenly court—that is, in the heavenly sanctuary, next to the Father, an indication that the judgment on earth was but an expression of the real judgment that would take place in heaven. God would judge the false teachers and leaders in Israel.
This explains why the call to repentance, a common feature in the previous speeches in Acts (Acts 2:38, Acts 3:19, Acts 5:31), is missing here. Israel’s theocracy was coming to an end, meaning that the world’s salvation would no longer be mediated through national Israel as promised to Abraham (Gen. 12:3, Gen. 18:18, Gen. 22:18), but through the followers of Jesus, Jew and Gentile, who were now expected to leave Jerusalem and witness to the world (Acts 1:8).
Stoning was the penalty for blasphemy (Lev. 24:14), though it is not clear whether Stephen was sentenced to death or lynched by a crowd of fanatics. At any rate, he was the first recorded believer in Jesus to be killed because of his faith. That the witnesses laid their garments at Saul’s feet suggests he was the leader of Stephen’s opponents; yet, when Stephen prayed for his executioners, he prayed for Saul, as well. Only a person with a superior character and unwavering faith could do such a thing, a powerful manifestation of his faith and the reality of Christ in his life.
Source: Daily Sabbath School Lessons