Albert Barnes on Matthew 21:43

The kingdom of God, etc. Jesus applies the parable to them--the Jews. They had been the children of the kingdom, or under the reign of God; having his law, and acknowledging him as King. They had been his chosen and peculiar people. But he says that now this privilege should be taken away, and they cease to be the peculiar people of God; and the blessing should be given to a nation who would bring forth the fruits thereof, or be righteous; that is, to the Gentiles, Acts 28:28.