Where does Joshua repeat the promise about Israel's land borders?
The repetition appears in Joshua, verse 4, where Israel's borders extend from the wilderness and Lebanon to the great river Euphrates, include all the Hittite land, and reach westward to the Mediterranean Sea. This restates the earlier promise Moses repeated, covering the whole Middle East.
Les explains that this is the third time the land-border promise is given: Moses repeated it, and now Joshua repeats it in Joshua, verse 4. The boundary runs from the wilderness and Lebanon to the great river Euphrates, through all the land of the Hittites, and westward to the Mediterranean Sea. In the surrounding context, the full extent is described as the whole Middle East—from northern Lebanon beyond Mount Hermon to the Euphrates, down to the Persian Gulf and the Red Sea, and across to the river of Egypt. Les stresses that when Christ returns, Israel will have the whole Middle East, and it will be like the Garden of Eden, not desert sand. He also notes the Old Testament was addressed to the Jew, yet a statement like God's promise “I will not fail thee, nor forsake thee” can still be applied personally.
From the wilderness and this Lebanon even unto the great river, the river Euphrates, all the land of the Hittites, and unto the great sea toward the going down of the sun, shall be your coast.