Deu 7:1 “When the LORD your God brings you into the land that you are entering to take possession of it, and clears away many nations before you, the Hittites, the Girgashites, the Amorites, the Canaanites, the Perizzites, the Hivites, and the Jebusites, seven nations more numerous and mightier than you, and when the LORD your God gives them over to you, and you defeat them, then you must devote them to complete destruction. You shall make no covenant with them and show no mercy to them. You shall not intermarry with them, giving your daughters to their sons or taking their daughters for your sons, for they would turn away your sons from following me, to serve other gods. Then the anger of the LORD would be kindled against you, and he would destroy you quickly. But thus shall you deal with them: you shall break down their altars and dash in pieces their pillars and chop down their Asherim and burn their carved images with fire.
Joshua 6:17 And the city and all that is within it shall be devoted to the LORD for destruction.
Joshua 10:30 And the LORD gave it also and its king into the hand of Israel. And he struck it with the edge of the sword, and every person in it; he left none remaining in it. And he did to its king as he had done to the king of Jericho.
Joshua 10:42 And Joshua captured all these kings and their land at one time, because the LORD God of Israel fought for Israel.
Joshua 21:44 And the LORD gave them rest on every side just as he had sworn to their fathers. Not one of all their enemies had withstood them, for the LORD had given all their enemies into their hands.
Deuteronomy 23:14 Because the LORD your God walks in the midst of your camp, to deliver you and to give up your enemies before you, therefore your camp must be holy, so that he may not see anything indecent among you and turn away from you.
Israel wasn’t in the land yet, but Moses still instructed them as if it were a certainty. This was based on the faithful promise of God, but it was also according to His principle of preparation. “Sure,” Moses said, “the Canaanite nations are greater and mightier than you. But they are not greater and mightier than God.” God brought Israel to face a challenge that was impossible in their own strength – but entirely possible in Him. God could be counted on. Yet, God would not do it all for them. The extent of the work would depend on their faithful response to what God would do.
This principle of battle until absolute victory is the key to victory as we take the Promised Land of blessing and peace God has for us in Jesus. We show no mercy to our enemies in the land, but we destroy them utterly. Many of us, truth be told, simply do not want to completely destroy the sins which keep us from God’s Promised Land of blessing and peace – we want to weaken them, and have some control over them, but we do not want to utterly destroy them. (Guzik)
Here is a strict caution against all friendship and fellowship with idols and idolaters. Those who are in communion with God, must have no communication with the unfruitful works of darkness. Limiting the orders to destroy, to the nations here mentioned, plainly shows that after ages were not to draw this into a precedent. A proper understanding of the evil of sin, and of the mystery of a crucified Saviour, will enable us to perceive the justice of God in all his punishments, temporal and eternal. We must deal decidedly with our lusts that war against our souls; let us not show them any mercy, but mortify, and crucify, and utterly destroy them. (Henry)