Charles Ellicott Commentary Isaiah 51:2

"Look unto Abraham your father, and unto Sarah that bare you; for when he was but one I called him, and I blessed him, and made him many." — Isaiah 51:2 (ASV)

I called him alone. —Literally, as one. If so great a nation had sprung from one man (Hebrews 11:12), so would God out of the faithful remnant once more create a people. (Compare to Ezekiel 33:24, where the exiles are represented as boastfully inverting the argument: “Abraham was one, and we are many; therefore we shall prosper, the chances are in our favour.”)