Thomas Aquinas

In the waters: "the waters would burn with fire," because you are all fiery, if you should wish: "at another time the fire, above its own power, burnt in the midst of water" (Wis 16:19); or, by the waters are signified peoples: "the many waters are many peoples" (Rev 17:15). The effect on men, and first, on the gentiles: "that the nations might tremble at your presence": "the Gentiles shall be troubled" (Ps 65:7-8); literally, they will be shaken; or this refers to the conversion of the gentiles after the coming of Christ.

Commentary on Isaiah ↗