Why couldn't the Kingdom come until the Gentile complement was completed?
According to Ephesians 1:10, the Kingdom could not arrive until the Gentile complement—the Church—was completed because the coming Kingdom economy gathers all things under Christ’s headship. It includes both Israel’s earthly kingdom and the heavenly Body of Christ, so the heavenly people had to be completed first.
Les explains that the Old Testament promised a glorious, earthly Kingdom—Heaven on earth—with Christ as King. The King was in Israel’s midst, and Israel was being offered entrance into those earthly promises. Yet, according to Ephesians 1:10, that Kingdom could not come until the Gentile complement, which was the Church, had also been completed. When the Kingdom economy is entered, everything comes under Christ’s headship: the earthly people Israel with their earthly Kingdom, and the heavenly people, the Body of Christ. So the heavenly Body had to be completed first. Les then sets the Body of Christ aside for a later time and turns to Matthew 19, where Jesus is in His earthly ministry, proclaiming to Israel that He is Messiah and proving it with miracles, signs, and wonders. Peter responds by saying they have forsaken all and followed Him, asking what they will have.
That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him: