Isaiah 61:4 - Ellicott's Commentary On The Whole Bible

They shall build the old wastes... — Literally the waste places of olden time: i.e., not merely the cities that had fallen into ruins during the exile, but those that had been lying waste for generations. The words are parallel with those of Isaiah 58:12. By some commentators strangers is supplied from Isaiah 61:5 as the implied subject, as in Isaiah 60:10. Here, however, it would seem as if the prophet looked on the rebuilding as being Israel’s own work, while service of another kind was assigned to the aliens.