Isaiah 51:2

“Look unto Abraham your father, &c.] Not only the father of the Jewish nation, but of all them that believe: this explains what is meant by the rock, in the former verse, who is to be looked unto for imitation in the exercise of faith, and performance of duty, and for encouragement in distressed times and circumstances: and unto Sarah that bare you; signified by the pit or cistern; who was not only the mother of the Jewish nation; but such also are her daughters who do well, and tread in her steps: now the very unpromising circumstances these two persons were in, are proposed to be considered by the church in her present ones, for the encouragement of her faith; that as a numerous issue…”

“alone--translate, "I called him when he was but one" (Eze 33:24). The argument is: the same God who had so blessed "one" individual, as to become a mighty nation (Gen 12:1; Gen 22:7), can also increase and bless the small remnant of Israel, both that left in the Babylonish captivity, and that left in the present and latter days (Zac 14:2); "the residue" (Isa 13:8-9).”

“Look unto Abraham - What was figuratively expressed in the former verse is here expressed literally. They were directed to remember that God had taken Abraham and Sarah from a distant land, and that from so humble a beginning he had increased them to a great nation. The argument is, that he was able to bless and increase the exile Jews, though comparatively feeble and few. For I called him alone - Hebrew, ‘For one I called him;’ that is, he was alone; there was but one, and he increased to a mighty nation. So Jerome, Quia unum vocavi eum. So the Septuagint, Ὅτι εἷς ἦν hoti heis ēn - ‘For he was one.’ The point of the declaration here is, that God had called one individual - Abraham -…”

“Him alone - To follow me to an unknown land: him only of all his kindred. Increased - Into a vast multitude, when his condition was desperate in the eye of reason. And therefore God can as easily raise his church when they are in the most forlorn condition. Isaiah 51:3”

“51:2 Abraham . . . became a great nation: The exiled community had decreased in number. They needed to have faith that God could restore them again to a healthy and thriving population.”

“unto Abraham: Gen 15:1, Gen 15:2, Gen 18:11-13; Jos 24:3; Rom 4:1-5, Rom 4:16-24 for: Gen 12:1-3, Gen 13:14-17, Gen 15:4, Gen 15:5, Gen 22:17, Gen 24:1, Gen 24:35; Neh 9:7, Neh 9:8; Eze 33:24; Gal 3:9-14; Heb 11:8-12 Isaiah 51:3”