What point was Stephen making about Jesus' first and second coming?
Stephen was showing that Israel's rejection of Jesus at His first coming did not cancel God's program; the Messiah had died, risen, ascended, and was ready to return the second time if Israel would believe He is who He claimed to be. Stephen, like the Jews, did not envision a 2,000-year interval.
Les explains that Stephen is driving home the point that Jesus came to Israel the first time in His earthly ministry, and they rejected Him. But now He is ready to come the second time if they will just believe that He is who He says He is. Stephen does not see a 2,000-year interlude. Stephen stands in the same position as the Jews Les has on the board: they expected that since Christ had died, been raised, and ascended, everything was set for Him to come back if Israel would just believe. Les then calls attention to the allegory or typology regarding Moses in Acts chapter 7, beginning at verse 23, where Moses at forty years old came into his heart to visit his brethren, the children of Israel.