John 8:37 "I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you."
The Jewish people were direct descendants of Abraham. However, as with so many biblical truths, there was much more to the Abrahamic covenant than what a casual glimpse would reveal. In truth, these Jews were not actually a part of the spiritual children of Abraham.
The Holy Spirit revealed through the Apostle Paul in Galatians 3:16 and 29 that God's covenant was to Abraham and his singular "seed" or descendant, which was Christ. No one ever became an heir of God's promises through his natural birth. Before Jesus gave Himself as an offering for our sin, the Old Testament saints were justified by faith in God's promises concerning the Messiah who was yet to come. After Jesus' death and resurrection, New Testament saints are justified by faith in what Jesus has already accomplished. No one has ever been saved because of who his parents are.
Those who have been born again through faith in Jesus have been circumcised in their heart (Colossians 2:11-12) and are the true Jews. They aren't Jews in nationality or religion, but they are the true people of God. Gentiles who are united with Christ in the new birth are now God's people. Anyone who is saved through faith in Jesus is now Abraham's seed and heirs according to the promise (Galatians 3:16, 22, 26-29). This leaves no doubt that the Church is now God's chosen people on earth. This does not mean that God has forsaken the Jews. There are still prophesies which apply to the physical nation of Israel which will be fulfilled. However, the New Testament Church, composed of Jews and Gentiles, is now God's kingdom on earth. We are all His.