What opportunity did Israel miss?
Israel missed the opportunity to be a kingdom of priests and a holy nation, to receive the king and the kingdom, and to bring all the nations of the world to a knowledge of God. Instead, in unbelief they rejected the king and the kingdom, dropped the ball, and were dispersed.
Les teaches that Exodus 19 states God would make Israel a kingdom of priests and a holy nation. Putting them under law was to prepare them for that tremendous role. When the opportunity came, they could have had the king and the kingdom and brought all nations to a knowledge of their God, but they dropped the ball and blew it. In unbelief they rejected the king and the kingdom. As a result, they were dispersed into the world, lost their temple and worship, and God turned to the Gentiles without using the nation of Israel. Les also notes the 144,000 Jews will get a taste of what the nation as a whole missed, going to every tongue, tribe, and nation so a multitude comes to salvation through their ministry, and they will be martyred.