For so ... - Paul, as usual, appeals to the Scriptures to justify his course. Here he appeals to the Old Testament rather than to the command of the Saviour, because the Jews recognized the authority of their own Scriptures, while they would have turned in scorn from the command of Jesus of Nazareth.
I have set thee ... - I have constituted or appointed thee. This passage is found in Isaiah 49:6. See the notes on Isaiah 49:1-6.
To be a light - See the notes on John 1:4.
Of the Gentiles - This was in accordance with the uniform doctrines of Isaiah, Isaiah 42:1; Isaiah 54:3; Isaiah 60:3, Isaiah 60:5,Isaiah 60:16; Isaiah 61:6, Isaiah 61:9; Isaiah 62:2; Isaiah 66:12; compare Romans 15:9-12.
For salvation - To save sinners.
Unto the ends of the earth - To all lands; in all nations. See the notes on Acts 1:8.