Jamieson, Fausset and Brown on Obadiah 1:19

19. they of the south--The Jews who in the coming time are to occupy the south of Judea shall possess, in addition to their own territory, the adjoining mountainous region of Edom.

they of the plain--The Jews who shall occupy the low country along the Mediterranean, south and southwest of Palestine, shall possess, in addition to their own territory, the land of "the Philistines," which runs as a long strip between the hills and the sea.

and they shall possess the fields of Ephraim--that is, the rightful owners shall be restored, the Ephraimites to the fields of Ephraim.

Benjamin shall possess Gilead--that is, the region east of Jordan, occupied formerly by Reuben, Gad, and half Manasseh. Benjamin shall possess besides its own territory the adjoining territory eastward, while the two and a half tribes shall in the redistribution occupy the adjoining territory of Moab and Ammon.