What opportunity is Israel being offered while the King is in their midst?
While the King is in their midst, Israel is offered the opportunity to enter into all the earthly promises of the glorious Kingdom that will come to fruition, with Christ as King on earth. This offer is part of God's promised earthly kingdom.
Les explains that the Old Testament foretold a glorious Kingdom on earth—Heaven on earth—with Christ as King. Because the King is in the midst of Israel, they are being offered the opportunity to enter into all these earthly promises which are going to come to fruition. However, even according to Ephesians 1:10, that could not happen until the Gentile complement, the Church, had also been completed. When the Kingdom economy comes, everything will come under Christ's headship: the earthly people of Israel and their earthly Kingdom, along with the heavenly people, the Body of Christ. Les then moves to Matthew 19, where in His earthly ministry Jesus had been proclaiming to Israel that He is the Messiah, proving it with miracles, signs, and wonders, and Peter asks what they will have for forsaking all and following Him.