“set you as a covenant.” See commentary on Isaiah 49:8.
“a light for the nations.” The salvation and everlasting life given by the Messiah was not just for the Jews, even though many of them thought that it was. The first prophecy of the Messiah is the one God made to Adam and Eve in the Garden of Eden in Genesis 3:15, and that was thousands of years before the Jews existed. About 2000 years after that first prophecy of the Messiah, God promised Abraham that all the people of earth, not just the Jews, would be blessed through him (Gen. 12:3). Then God repeated that promise to Isaac (Gen. 26:4); and to Jacob (Gen. 28:14). Besides those promises, the Old Testament had a number of verses that spoke of Gentiles being included in the Messianic Kingdom, which meant they were granted everlasting life (Ps. 102:15; Isa. 2:2-4; 19:23-25; 42:6; 49:6; 51:4-5; 56:3-7; 60:3; 66:18-21; Ezek. 39:21, 27; Micah 4:2; Hag. 2:7; Zech. 8:22).