en_tn/isa/42/06.md

have called you

Here "you" is singular and refers to Yahweh's servant. (See: rc://en/ta/man/jit/figs-you)

I will ... set you as a covenant for the people

Here the word "covenant" is a metonym for the one who establishes or mediates a covenant. Alternate translation: "I will ... make you be the mediator of a covenant with the people" (See: rc://en/ta/man/jit/figs-metonymy)

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. (See: rc://en/ta/man/jit/figs-metaphor)