From E. J. Young’s three-volume Isaiah commentary, Vol. 3, pages 120–1, on :
The language is striking, for the servant is actually identified as a covenant. A covenant, however, in this instance is not a pact or agreement between two equal parties. From the parallel word light (i.e. salvation), we learn that it is actually a divine bestowal of Grace. God sovereignly bestows to man His blessings of salvation and it is this sovereign dispensation that is called a covenant.
That the servant is identified with the covenant of course involves the idea of his being the one through whom the covenant is mediated, but the expression implies more. In form it is similar to our Lord’s “I am the resurrection and the life,” or the phrase in 49:6, “to be my salvation.” To say that the servant is a covenant is to say that all the blessings of the covenant have their root and origin in, and are dispensed by him. … Moses was a mediator of a covenant but the servant is the covenant. In New Testament terms, this means that they to whom God sovereignly bestows the grace of salvation receive the servant Himself.
6 “I am the Lord; I have called you in righteousness;
I will take you by the hand and keep you;
I will give you as a covenant for the people,
a light for the nations, (ESV)