Jos 16: "The record continues the listing of inheritances, as
Joshua sets out the landmarks that constitute the gift of Yahweh to His people.
This chapter sets out the inheritance of Joseph who has two sons, Ephraim and
Manasseh, and consequently stood as recipient of the divine firstborn, receiving
a double portion of inheritance. Joseph was elevated to the firstborn instead of
Reuben (1Ch 5:1). So Joshua sets out:  The general borders: vv 1-4. 
Ephraim's border: vv 5-9.  Ephraim's failure: v 10. The rest of the
inheritance of Joseph's sons continues in Jos 17.
"As with the other tribes, so with Ephraim: they failed to
fulfil the instruction of their commander: see Jos 16:10. It seems that although
Joshua ejected the main power of the Canaanites, they returned to their former
cities, whilst he completed the campaign elsewhere. This required that each
tribe make its own effort to obtain its individual holding, although the land as
a whole had been won for Israel. In like manner Christ has opened the way to
life eternal, but we each must conquer our individual inheritance"