What still has to happen because Israel rejected the kingdom?
Because Israel did not accept the offered King and kingdom, Elijah must still come. The Old Testament said Elijah had to come before Christ's return or the kingdom's establishment. Since Israel did not accept it, John was not the Elijah in that present fulfillment, and Elijah remains yet to come—likely as one of Revelation's two witnesses.
Les explains that Jesus genuinely offered Himself as Israel's King and the kingdom in fulfillment of the Old Testament covenants, including the Abrahamic covenant. The offer was valid, though prophecy required Christ to die first. Jesus said that if Israel received the kingdom at that time, John would be the prophesied Elijah. But since Israel did not accept the kingdom, Elijah still has to come. Les teaches from Revelation chapter 11 that one of the two witnesses will quite likely be the Old Testament Elijah, brought back on the scene.