Isaiah 8:7 - Matthew Poole's English Annotations on the Holy Bible

Therefore; because they despise the opposition which they have from Shiloah and Jerusalem, they shall have a more potent enemy. Upon them; upon Israel. See on the foregoing verse. Of the river of Euphrates, oft called the river, for its eminent greatness; whereby he understands the Assyrian forces, as the next words explain the metaphor. All his glory; his numerous and puissant army, in which he gloried. See Isaiah 10:8. He shall come up over all his channels; this great river shall overflow its own proper channels. The meaning is, This great monarch shall enlarge his dominions, and add the lands of Syria and Israel to them. Some render the words, he shall come up with all his channels or streams; for the Hebrew particle all sometimes signifies with, as Job 38:30. But it seems hard to understand the same particle one way in this clause, and another in the last clause. Besides, the last clause favours the former interpretation, the same thing being repeated in it, as is usual in the sacred writings. Or this may be understood of the channels and banks of the people or land of Israel. The enemy being represented under the metaphor of a river breaking in upon their land, may fitly be said to overflow all their channels and banks, to wit, all places, both low and high, so that nothing shall be able to withstand his fury.