Jamieson, Fausset and Brown on Isaiah 5:17

17. after their manner--literally, "according to their own word," that is, at will. Otherwise, as in their own pasture [Gesenius]: so the Hebrew in Mi 2:12. The lands of the Scenite tent dwellers (Jr 35:7). Arab shepherds in the neighborhood shall roam at large, the whole of Judea being so desolate as to become a vast pasturage.

waste ... fat ones--the deserted lands of the rich ("fat," Psa 22:29), then gone into captivity; "strangers," that is, nomad tribes shall make their flocks to feed on [Maurer]. Figuratively, "the lambs" are the pious, "the fat ones" the impious. So tender disciples of Jesus Christ (Joh 21:15) are called "lambs"; being meek, harmless, poor, and persecuted. Compare Eze 39:18, where the fatlings are the rich and great (1Co 1:26, 27). The "strangers" are in this view the "other sheep not of the" the Jewish "fold" (Joh 10:16), the Gentiles whom Jesus Christ shall "bring" to be partakers of the rich privileges (Ro 11:17) which the Jews ("fat ones," Eze 34. 16) fell from. Thus "after their (own) manner" will express that the Christian Church should worship God in freedom, released from legal bondage (Joh 4:23; Ga 5:1).