This shall be your south coast. — This phrase does not seem to fit in with the language of the rest of the passage. But it is extremely like a reminiscence of the language of Moses in Numbers 34:3; Numbers 34:6; Numbers 34:9; Numbers 34:12. “This book of the law shall not depart out of thy mouth” was the instruction to Joshua, and in describing the border of Judah, he is really describing also the southern border of all Israel; and he does it throughout in language very like that of Moses in Numbers 34. But Moses wrote it in the second person and in the future tense throughout; Joshua wrote it in the third person and in the past tense, with this one exception, in which he seems to have unconsciously adopted the phraseology of the lawgiver instead of the historian.
Related Commentaries of Joshua 15:4
Joshua 15:4
4 From thence it passed toward Azmon, and went out unto the river of Egypt; and the goings out of that coast were at the sea: this shall be your south coast.