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 - and that he had caused him to increase until a mighty nation had sprung from him, and that he had the same power to increase the little remnant that remained in Babylon until they should again become a mighty people.