These verses conclude the account of the division of the land proper (chs13-21; cf. Joshua 1:2-6; Joshua 11:23). They bind the two parts of the second half of the book together, and they form a theological conclusion to the entire book up to this point. [source][source][source]
These statements may seem at first to mean that at this time the Israelites had obtained everything God had promised the patriarchs. Such was not the case. [source][source][source]
"Notwithstanding the fact that many a tract of country still remained in the hands of the Canaanites, the promise that the land of Canaan should be given to the house of Israel for a possession had been fulfilled; for God had not promised the immediate and total destruction of the Canaanites, but only their gradual extermination (Ex. xxiii29 , 30; Deut. vii22). And even though the Israelites never came into undisputed possession of the whole of the promised land, to the full extent of the boundaries laid down in Num. xxxiv1-2 , never conquering Tyre and Sidon for example, the promises of God were no more broken on that account than they were through the circumstance, that after the death of Joshua and the elders his contemporaries, Israel was sometimes hard pressed by the Canaanites; since the complete fulfillment of this promise was inseparably connected with the fidelity of Israel to the Lord." [1][source]
"The Canaanites, it is true, were yet in possession of some parts of the country, but they were so far subdued, that they gave them [2] no serious molestation, and they were enabled to sit down in their possessions in the enjoyment of comparative rest and quiet. They had as much of the land in actual possession as they could occupy; and as they increased God enabled them, according to his promise, Exodus 23:30, to carry forward the work of extermination, and obtain further room for their settlement. All the assurances given to Joshua , ch15 , of a successful tide of victories during his life, were accomplished, and as to the subsequent annoyance and occasional prevalence of their enemies, it was owing solely to the supineness and infidelity of Israel. So long as they were obedient, they were uniformly triumphant and prosperous." [3][source]
In Deuteronomy 26:5-1006 Joshua indicated that there was more land that the Israelites needed to possess. In Joshua 24:1-28 he urged the people to commit themselves anew to the Mosaic Covenant so they might possess and experience all that God had promised their forefathers. These passages confirm that Joshua did not mean by his statement of God"s faithfulness here that Israel had already possessed all that God had promised her forefathers. [source][source][source]
"The meaning of the Deuteronomist"s rest theology is clearly seen here [4]. Rest is peace, absence of enemies and war. See Joshua 1:12-18. The verse is a counterpart to chap12 , which concluded the first section of the book. It is the fulfillment of God"s promise in Exodus 33:14. Both major sections of the book thus end with a statement about God"s faithfulness in totally defeating the enemy." [5][source]
The point Joshua was making in Joshua 21:45 was that God had been faithful to His promises up to that moment. He had promised possession of the land, rest on every side, and victory over enemies. Israel had experienced all of these to some degree. God had been faithful to the "good promises" He had made to them when they had prepared to cross the Jordan ( Joshua 1:1-9). [source][source][source]
It was common among the Semites to regard a part of the whole as the whole (cf. 1714271910_4; 1 Kings 13:32; Jeremiah 31:5; 2 Samuel 5:6-10; Revelation 14:1; Revelation 22:2; Romans 15:19-24). The name for this viewpoint is representative universalism. Some students of this passage believe that Joshua was taking this view here. He was speaking in universal terms. He regarded the individual kings, towns, and areas that he had subdued as representative of the entire land of Canaan. [6][source]
"The small section summarizes the theological point of the book of Joshua. The entire book is to be read in light of these three verses, particularly the last." [7][source]