Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

Israel, when it has such cause as this for praising Jehovah, will have become a numerous people once more. "Thou hast added to the nation, O Jehovah, hast added to the nation; glorified Thyself; moved out all the borders of the land." The verb יסף, which is construed in other cases with על, אל ,, here with ל, carried its object within itself: to add, i.e., to give an increase. The allusion is to the same thing as that which caused the prophet to rejoice in Isa 9:2 (compare Isa 49:19-20; Isa 54:1., Mic 2:12; Mic 4:7; Oba 1:19-20, and many other passages; and for richaktâ, more especially Mic 7:11). Just as Isa 26:13 recals the bondage in Egypt, and Isa 26:14 the destruction of Pharaoh in the Red Sea, so Isa 26:16 recals the numerical strength of the nation, and the extent of the country in the time of David and Solomon. At the same time, we cannot say that the prophet intended to recall these to mind. The antitypical relation, in which the last times stand to these events and circumstances of the past, is a fact in sacred history, though not particularly referred to here.