“I am the LORD, I have called You in righteousness, I will also hold You by the hand and watch over You, And I will appoint You as a covenant to the people, As a light to the nations, (Isaiah 42:6)
I am the Lord. His personal name is the one he explained to Moses as specially symbolic of the unique relationship he bore to Israel. Here that covenant name guarantees his ministry through the Messiah-Servant.
Covenant for the people. The Servant is a covenant in that he personifies and provides the blessings of salvation to God’s people Israel. He is the Mediator of a better covenant than the one with Moses, i.e., the New Covenant.
Light for the nations. Simeon saw the beginning of this fulfillment at Christ’s first coming (Luke 2:32). He came as the Messiah of Israel, yet the Savior of the world, who revealed himself to a non-Jewish immoral woman by the well in Samaria and commanded his followers to preach the gospel of salvation to everyone in the world.
Certainly the church, made up mostly of Gentiles grafted into the trunk of blessing fulfills this promise, as does the future kingdom on earth when the Servant will use Israel to shine and enlighten all the nations of the earth.
Commentary by John MacArthur