‘ And Joshua said to them, “If you are a great people, get yourselves up to the forest and clear land for yourselves there in the land of the Perizzites and of the Rephaim, since the hill country of Ephraim is too narrow for you.” '
If Joshua had emphasised the size of their territory and their extra portion in Transjordan he would have engendered perpetual jealousy among the other tribes. But wisely he desisted. Instead he took up their own claim to be a great people. As they were a great people let them clear land in ‘the forest' where they only had to deal with village dwellers (Perizzites) and the Rephaim, thus making more land for themselves, land which had possibly not been included in the divisions.
The Perizzites were village dwellers. The Rephaim were a very tall people who engendered awe, but were in fact not on the whole very good fighters (Genesis 14:5; Deuteronomy 2:11; Deuteronomy 2:19-21). They had been driven out by the Moabites and Ammonites and possibly haunted the forests, flitting with their long thin forms between the trees. Indeed it may be that the later use of the word of spirits and ghosts (Psalms 88:10-11; Proverbs 2:18; Proverbs 9:18; Proverbs 21:16; Job 26:5; Isaiah 14:9; Isaiah 26:14; Isaiah 26:19) was in Joshua's mind, a contemptuous ‘village dwellers and ghosts'. In Phoenician tomb inscriptions rp'm was used in the sense of ghosts.
“The forest” was possibly a word that covered large swathes of forests just as ‘the mountain' meant the whole of the hill country. What he was pointing out was that there was much forest land on mountains that could be cleared. It might also refer to the wooded highlands on the east of Jordan next to Manasseh's territory there. That would certainly be something they had to climb to (from the Jordan valley). This would then be a discreet reminder of what they had been given in Gilead and Bashan. Verse 18 refers the forest to ‘hill country'. Both sides of the Jordan may in fact be in mind.