The people of Israel, during and after their Babylonian exile, were desperate for a word of consolation from God--for some sign that God had not abandoned them. Isaiah's words of prophecy addressed their pleas with the promise of a restored Kingdom. This Kingdom will be a light for the world, drawing all peoples to Jerusalem.
What Isaiah's message predicted would be different, however, from what the people of Israel had been expecting. They anticipated a mighty earthly Kingdom led by a Messiah (the Anointed One) who would be a great warrior. They wanted revenge against the foreign peoples who had humiliated and oppressed Israel. They wanted the kingdoms of the earth to come to Jerusalem as conquered slaves. But this would have made Israel no better than the pagan kingdoms of Babylon or Egypt.
Instead, what God provided in Jesus was the true Kingship: the reign of God that conquers the real enemies of humanity--sin and death. In Jesus the peoples of the world could receive not a conquering tyrant but a loving redeemer. He would pay the debt for their sins and the sins of Israel. He would welcome the gentiles as sons and daughters coequal not only with the Israelites, but with His Divine Self.
So we, who claim this common sonship with Christ Jesus, must be ready to welcome all men and women who honestly seek union with Him as our sisters and brothers. God's kingdom is bigger than we would make it ourselves, and that is a very good thing.