It seems God has rejected Israel, since they are rejecting Jesus.
But Elijah felt like that, too, when God had His remnant.
God is bringing Gentiles in, now, and they shouldn't be arrogant toward the Jews. The root supports you, and you are in by faith alone, not by how much better you are than the Jews.
They are disobeying for a time, that God's mercy later may be shown.
How this is about Jesus
He is the vine, we are the branches. The metaphor of the tree that Paul uses, where Jews are broken off the tree when they reject Jesus, fits John 15 exactly.
Jesus did come from the stump of Jesse, the root of Abraham and David. The deliverer came from Zion.
We do well to study the history of the Jews (I recommend Paul Johnson's history). Instead of disdaining and rejecting them as either legalistic Pharisees (Orthodox) or liberals, find the good. "As a Driven Leaf" by Milton Steinberg is good.