What Is an Allegory in Galatians 4?

In Galatians 4 verses 21 through 31, Paul says that this story that we read in Genesis 16 between Abram and Hagar and Sarai is an allegory. The basic meaning of an allegory is to put something spiritual in for something material and then to extend that into a story. We ought not presume the kindness of his grace in Romans 2. And just one quick observation, the way this is connected to Genesis 926 where we have the curse on Canaan. So it's like the Lord is saying he's working out his plan for human history through Abraham and his children.