# have called you
Here "you" is singular and refers to Yahweh's servant.
# I will ... set you as a covenant for the people
"I will ... make you be the mediator of a covenant with the people"
# a light for the Gentiles
Yahweh speaks of making his servant the one who delivers the nations from bondage as if he were making him a light that shines in dark places for the Gentiles.