Va'etchanan - Sh'vi'i
Intermarriage and Assimilation
Moshe told the nation that God was about to bring them into the land of Israel. The seven Canaanite nations currently occupying the land are, objectively speaking, larger and more powerful than the Jews, but God will enable them to defeat their enemies. They must drive them out or destroy them; they may not make peace treaties with them.
Intermarriage with non-Jews is prohibited and a fast track to assimilation. If a Jewish man does marry a non-Jewish woman, the children of that union will not be Jewish. (See Talmud Kiddushin 67b and Rashi there.) The idols and altars of the Canaanite nations must be destroyed.
God didn't pick Israel because they're the biggest nation - if anything, they're one of the smallest! Rather, God loves them and He fulfills the promise He made to their Forefathers.
Know that God is the only Power. He is faithful to keep His side of the covenant and He remembers those who show their love for Him by following His Torah. Those who show disdain for Him, however, will know His displeasure. So be among the people in the former category.