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.

“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)