Albert Barnes Commentary Joshua 17:15

"And Joshua said unto them, If thou be a great people, get thee up to the forest, and cut down for thyself there in the land of the Perizzites and of the Rephaim; since the hill-country of Ephraim is too narrow for thee." — Joshua 17:15 (ASV)

Joshua was himself of the tribe of Ephraim, but far from supporting the demands of his kinsmen, he reproves them and calls upon them to make good their great words by corresponding deeds of valor. He bids them clear the country of its woods and thus make room for settling their people.

The “wood country” probably means the range that runs along the northern border of Manasseh and connects the mountains of Gilboa with Carmel. Mount Ephraim, (a name perhaps used by anticipation) called “the hill” (Joshua 17:16) and “the mountain of Israel” (Joshua 11:16), is the eastern portion of the territory of Ephraim and Manasseh extending toward the Jordan. This was a hilly, though by no means barren, district.