Jamieson, Fausset and Brown on Isaiah 8:6

6. waters of Shiloah ... softly--Their source is on the southeast of Zion and east of Jerusalem. It means "sent," the water being sent through an aqueduct (Joh 9:7). Figurative for the mild, though now weak, sway of the house of David; in the highest sense Shiloah expresses the benignant sway of Jehovah in the theocracy, administered through David. Contrast to the violent Euphrates, "the river" that typifies Assyria (Is 8:7; Re 17:15). "This people" refers both to Israel, which preferred an alliance with Rezin of Syria to one with the kings of Judah, and to Judah, a party in which seems to have favored the pretentions of the son of Tabeal against David's line (Is 7:6); also to Judah's desire to seek an Assyrian alliance is included in the censure (compare Is 7:17). Is 8:14 shows that both nations are meant; both alike rejected the divine Shiloah. Not "My people," as elsewhere, when God expresses favor, but "this people" (Is 6:9).