In Romans Chapter 11, Paul continues to expound on the fact that God has not rejected Israel. Rather, there is still a remnant and in fact always has been. Paul himself was a Jew. Just as God advised Elijah that he was not the last prophet but that he had reserved 7000, so today they is still a remnant maintained by His grace.
Hard hearts
The Jewish people rejected Christ because of their hard hearts. Isaiah prophecied about this and Christ quotes him when HE tells the Jews they refuse to listen. The Jews tried to be righteous through obeying the Law but, as we have read throughout Romans, it is by faith in Christ alone that saves. The Jews, even today, know about Jesus but they refuse to accept Him. Their eyes are still blinded. There attitude of the heart is to reject what God has said and so God will allow them to continue on this path of a hardened heart.
The tree
Because of their unbelief, the Jews have been removed from the tree but God didn’t cut down the whole tree. He removed some branches but there are still many Jews who, by faith, believe in Christ. We Gentiles, wild branches, have been grafted into this tree. The tree is the spiritual Israel.
Pruning
As God removed those Jews who did not believe, He will also graft them back in when they believe. In fact, Paul says that the whole nation. all of Israel, will in the future turn to Jesus! He also warns us, the believer that we have to to continue in our believe in Jesus. Otherwise, we will be removed.
Here is the YouTube video on Romans Chapter 11