When you read this prophecy in Genesis 25:23, it’s essential to see this correctly.  In the stories of Isaac/Ishmael and Jacob/Esau, the older will serve the younger.  But we could also say the first will serve the last.  Just because something comes first in order does not mean it’s first in prominence.  

Think of Adam.  Adam is called the first Adam.  Jesus is called the last Adam.  See?  

The world’s system values the order of things: first in class, firstborn, and first in position.  God values something else.