What does Isaiah 23:4 mean?
The great trading city of Tyre has fallen. This ancient city has been completely wiped out by an enemy. This prediction from Isaiah points forward to the Lord's judgment on the wealthy city. Tyre's fall will bring grief to many. This includes those in the nearby Phoenician region who benefited financially from trade. It also affects trading partners like those in Egypt who shipped their grain through Tyre (Isaiah 23:1–3). Now his audience learns that the sea will also mourn.It's unclear why Isaiah writes that Sidon, a partner city to Tyre, should be ashamed for mourning. The point may be that "the sea," in a symbolic sense, has suffered even greater loss. Some commentators understand the word for "stronghold" or "fortress" to be a reference to Yam, the Canaanite god of the sea.
Isaiah paints a picture of the sea grieving the loss of the sailors that travelled its waters from Tyre. After all, the ocean has no children of its own. It has not raised boys and girls. The sailors of Tyre lost in the battle were viewed as its children, and now they are gone. The oceans waters are now empty of these people they once carried to distant shores.