Why did God separate Abraham from the mainstream of humanity when He called him out of Ur?

Les explains that as soon as Abraham was called out of Ur of the Chaldees, God separated him from the mainstream of humanity. God promised that out of that one man would come a distinctive race and nation, the nation of Israel. What made them distinctive was that from the very onset of the promise to Abraham until they were finally dispersed after rejecting their king, Israel had it constantly drummed into their mindset that they were a special, called-out, separated, covenant people of God, and all their promises are earthly. Thus they are God's earthly people. Les also clarifies that this does not mean Old Testament saints stayed on earth; a believer went to paradise. But Israel's promises and resurrection are earthly, not heavenly. Abraham himself was a wealthy man, reflecting that earthly focus.