Albert Barnes Commentary Exodus 23:31

"And I will set thy border from the Red Sea even unto the sea of the Philistines, and from the wilderness unto the River: for I will deliver the inhabitants of the land into your hand: and thou shalt drive them out before thee." — Exodus 23:31 (ASV)

In Exodus 23:23, the limits of the Land of Canaan, strictly so called, are indicated; to this, when the Israelites were about to take possession of it, the regions of Gilead and Bashan on the left side of the Jordan were added (Numbers 32:33–42; Joshua 13:29–32). These two portions made up the holy land, whose limits were recognized, with inconsiderable variations, until the final overthrow of the Jewish polity. But in this verse the utmost extent of Hebrew dominion, as it existed in the time of David and Solomon, is set forth.

The kingdom then reached to Eloth and Ezion-geber on the Elanitic Gulf of the Red Sea (1 Kings 9:26) and to Tiphsah on the “River” (that is, the River Euphrates) (1 Kings 4:24), with “the Sea of the Philistines” (that is, the Mediterranean) as its western boundary, and “the desert” (that is, the wildernesses of Shur and Paran) as its southern boundary (Deuteronomy 1:7; Deuteronomy 11:24; Joshua 1:4).