Jamieson, Fausset and Brown on Job 6:19

19. the troops--that is, "caravans."

Tema--north of Arabia-Deserta, near the Syrian desert; called from Tema son of Ishmael (Ge 25:15; Is 21:14; Jr 25:23), still so called by the Arabs. Job 6:19, 20 give another picture of the mortification of disappointed hopes, namely, those of the caravans on the direct road, anxiously awaiting the return of their companions from the distant valley. The mention of the locality whence the caravans came gives living reality to the picture.

Sheba--refers here not to the marauders in North Arabia-Deserta (Job 1:15), but to the merchants (Eze 27:22) in the south, in Arabia-Felix or Yemen, "afar off" (Jr 6:20; Mt 12:42; Ge 10:28). Caravans are first mentioned in Ge 37:25; men needed to travel thus in companies across the desert, for defense against the roving robbers and for mutual accommodation.

The companies ... waited for them--cannot refer to the caravans who had gone in quest of the waters; for Job 6:18 describes their utter destruction.