This passage refers to the gathering after (in this passage) Yahweh’s redemption of Israel. Along these mountain “ways” and along these exalted highways will travel the dispersed covenant people. The “north” is the direction from which they typically return. They are also gathered from the west and from “Sinim.” While different locations have been proposed for this land, some commentators propose that it might refer to a Jewish colony in Syene in southern Egypt. Westermann reviews the identification:
As long ago as 1775 Michaelis proposed to read Sewenim for the last word of the verse [Sinim]. Numerous editors have accepted the conjecture, and it has now been confirmed by the Isaiah MS. from Qumran. Thus, the reference is to the Jewish colony in Syene (Assuan) in the south of Egypt (cf. Ezek. 29:10, 30:6), which we know from the Elephantine papyri.