Jamieson, Fausset and Brown on Job 15:19

19. Eliphaz speaks like a genuine Arab when he boasts that his ancestors had ever possessed the land unmixed with foreigners [Umbreit]. His words are intended to oppose Job's (Job 9:24); "the earth" in their case was not "given into the hand of the wicked." He refers to the division of the earth by divine appointment (Ge 10:5; 25:32). Also he may insinuate that Job's sentiments had been corrupted from original purity by his vicinity to the Sabeans and Chaldeans [Rosenmuller].