Charles Ellicott Commentary Isaiah 33:21

"But there Jehovah will be with us in majesty, a place of broad rivers and streams, wherein shall go no galley with oars, neither shall gallant ship pass thereby." — Isaiah 33:21 (ASV)

A place of broad rivers and streams ... —Better, rivers and canals. The bold imagery has its starting-point in what the prophet had heard of the great cities of the Tigris and Euphrates. What those rivers were to Nineveh and Babylon, the same would the presence of Jehovah be to Jerusalem, which could boast only of the softly going waters of Shiloah (Isaiah 8:6).

Here, again, we have an echo of Psalm 46:4: There is a river, the streams whereof shall make glad the city of God. These words help us to understand the symbolism of Ezekiel’s vision of the river that could not be passed over, flowing out of the Temple (Ezekiel 47:1–5). And the spiritual river of the Divine Presence would have this advantage over those of which the great cities boasted, that no hostile fleet, no pirate ships, could use it for their attacks. So in Psalm 48:7 the ships of Tarshish are probably to be taken figuratively rather than literally for the Assyrian forces.