Forasmuch as this people. It is a question which people is intended, Judah or Israel. Ewald supposes Judah, and draws the conclusion that there was a strong party in Jerusalem which favored "the son of Tabeal."
Dr. Kay does the same, but understands the charge against Judah to be, not that it sympathized with Rezin, but that it fell into the same sins. Other commentators suggest that Israel is the people intended (as in Isaiah 9:16), the sense being carried on from Isaiah 8:4, where the word "Samaria" is suggestive of the Israelite people.
Refuseth the waters of Shiloah. The "pool of Siloah" (Nehemiah 3:15) was the tank or reservoir at the southwestern foot of Ophel, which is supplied with water by a narrow conduit cut through the limestone rock for a distance of 1750 feet from the "Pool of the Virgin" on the opposite side of Ophel, in the Kedron valley.
This pool itself is fed from reservoirs under the temple area, which have not yet been fully explored. It is probable that Isaiah uses the expression "waters of Shiloah" in a general sense for the streams, springs, reservoirs, conduits, which supplied the temple, and were connected with its service.
"Refusing the waters of Shiloah" would then be, without any violent metaphor, refusing the temple service and worship, which was exactly what the Israelites had done from the time of Jeroboam. That go softly.
In contrast with the "waters of the river, strong and many," of the next verse. They who refused the mild and gentle government of Jehovah should experience the impetuous and torrent-like rush of the Assyrian armies.
Rejoice in Rezin; rather, rejoice with Rezin; i.e. sympathize with him, rejoice when he rejoices.