How did Abraham become the father of the nation of Israel as a new race out of the mainstream of humanity?

God singled Abraham out in Ur of the Chaldees, gave him the covenant, and brought him out of the mainstream of humanity. Through Abraham, Isaac, and Jacob, God formed a separated race—the nation of Israel—no longer counted among the Gentile families. That distinctive call made Abraham the father of this new nation.

Les explains that Abraham was still part of the one race of people coming out of Adam, but God put His finger on Abraham in Ur of the Chaldees and gave him the covenant. At that point Abraham was brought out of the mainstream of humanity and became the father of a whole new race of people, the nation of Israel. This is why the lineage of Abraham, Isaac, and Jacob is studied: they bring about the nation of Israel as a separated race, no longer part of the Gentile families. Les defines a Jew as anyone from the bloodline of Abraham, Isaac, and Jacob and the twelve patriarchs; a Gentile is everybody else, whether Arab, Oriental, African, European, or American. The Jew came about because of that distinctive call of Abraham, “I will make of thee a nation of people,” a separated people off the main stream of humanity.

Genesis 12:1

Now the LORD had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father’s house, unto a land that I will shew thee:

What made Israel distinctive as a people?

Israel's distinctiveness came from being a special, called-out, separated covenant people of God. From the promise to Abraham until their dispersion after rejecting their king, they were constantly taught this identity, and all their promises were earthly, so they are called God's earthly people.