This was the confidence of so many of the Jewish people who did not understand the purpose of the national side of the Abrahamic covenant, and of the Mosaic covenant which followed. They believed they were a people favoured by God.
Those who base their hope on something other than the gospel of Jesus Christ need to be shown in the clearest terms that their trust is false. Part of the work of the evangelist is to pull down and destroy every false basis of hope, so that men and women are driven to the only true source of hope which God supplies. The Abrahamic covenant was a great blessing, but the carnal mind was quite capable of misusing it, and turning it into an obstacle to true understanding.