Romans 11:29 says "the gifts and the calling of God are irrevocable." In Romans 11:1-2 Paul says that "God has not rejected His people whom He foreknew." And in Romans 9:4 Paul says that God still has covenants (the Abrahamic and Davidic) and promises to fulfill with the Jewish people.
The Jewish people were chosen to be a vehicle of blessings to the nations (Genesis 12:1-3), and they have been. Through them God gave the world the Scriptures and the Messiah. They were also chosen to be witnesses of God (Isaiah 43:10-12). They remain a witness to this day. Their history shows that when you are faithful to God, He blesses; when you are unfaithful, He disciplines; and when you repent, He forgives and blesses again.
The Jews are currently under discipline, but before the end of the Tribulation, a remnant will repent and receive Jesus as their Messiah. Read Romans 9-11 and Zechariah 12:10 & 13:1.