Moses says that when the Lord brings them into the land and drives out seven nations greater and stronger than they (the Hittites, Girgashites, Amorites, Canaanites, Perizzites, Hivites and Jebusites), Israel must destroy them completely. They are to make no covenant or show no mercy to them, nor intermarry with them, because they would turn their children away from the Lord to serve other gods. They will tear down their altars, break their pillars and burn their images.
The reason is Israel's identity: they are a holy people to the Lord, chosen out of all peoples as his treasured possession. Moses explains that the Lord did not choose them because they were the most numerous, for they were the fewest of all peoples, but because he loved them and kept the oath he swore to their fathers. That is why he brought them out of Egypt with a mighty hand. The Lord is the faithful God who keeps covenant and steadfast love to a thousand generations of those who love him, but repays those who hate him.
If Israel obeys, the Lord will love and bless them: he will multiply their children, their fields and their flocks, and will keep sickness from them. Their gods would be a snare for Israel, and the people must not fear those nations. Moses encourages them to remember what the Lord did to Pharaoh, and assures them that he is in their midst, a great and awesome God, who will drive out those nations little by little. He ends with the command to burn the images of their gods and not covet their silver or gold, for they would be a trap and an abomination to the Lord.