How was God's calling of Abraham different from His earlier dealings?

God's call of Abraham marked a totally different phase: instead of dealing with the human race collectively through judgments and scattering like Babel, He began focusing on one set-apart chosen nation, Israel, beginning with Abraham, while allowing other nations to continue in their own pagan worship.

Les teaches that after the flood, Noah and his sons were instructed to set up human government to maintain law and order, something they did not have before. But about 175 years later the people rebelled at the Tower of Babel by congregating instead of scattering as God had instructed, so God confused their languages and scattered them. Then, about 150 years after Babel, God did something totally different again: He called out Abraham. Les explains that this marked a new break in God's dealings. Instead of dealing with the human race in the same way, God began to deal with one little chosen nation, Israel, set apart from the rest. The other nations were allowed to go on in their own pagan way and pagan worship, while God's focus narrowed to this set-apart nation beginning with Abraham.

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:

Why did God do something different and call Abraham after Babel?

After Babel’s language confusion, later generations became totally steeped in idolatry, even Abraham’s father Terah serving other gods in Ur. Therefore God did something different: He called Abraham out from that idolatry. Abraham became the man of faith, and God then left off dealing with Gentiles to deal with Jew only, with exceptions.