There are a number of reasons given in the Bible for why the people living in Canaan had to be exterminated. The most prominent reason in Deuteronomy is that if these people were left alive, they would turn the Israelites away from the Lord, encouraging them to serve other gods (Deuteronomy 7:4) and to engage in abominable practices (Deuteronomy 20:18). In Leviticus, the reason for the destruction of the Canaanites is the fact that they made the land itself unclean (Leviticus 18:24–25, Leviticus 18:27). In the book of Exodus, the primary reason for destruction is similar to that in Deuteronomy. The Canaanites must be driven from the land, else they will be a snare to Israel, encouraging them to sin and idolatry (Exodus 23:33; Exodus 34:15–16). In Genesis, we are told that the Lord was waiting for the sin of the Canaanite population to reach its limit before he brought judgment upon them (Genesis 15:16). The destruction of the Canaanites by the hands of Israel was therefore God’s judgment upon their sin. Finally, the book of Psalms also testifies that the destruction took place so that Israel could have a land in which they can serve God (Psalm 105:44–45).
20 For it was the LORD’s doing to harden their hearts that they should come against Israel in battle, in order that they should be devoted to destruction and should receive no mercy but be destroyed, just as the LORD commanded Moses.