God’s plan was to save the world. It was always His plan. And most likely this is the part of God’s plan that most caused the Jews to reject the Messiah. God gave hints throughout the Old Testament that this was His plan.
The priests and religious leaders and scholars wanted only Israel to be God's. They wanted to be the special and chosen. They didn’t want the entire world to be joined to God.
And the idea that God would allow others to join Him was appalling.
God’s plan from the very beginning was to save the world. And that’s what He did through Jesus.