See the Old and New Covenant play out in the life of Abraham
Gal 4:22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
Gal 4:23 But he who was of the bondwoman was born after the flesh; but he of the freewoman was by promise.
Gal 4:24 Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar.
As Abraham is the father of the faithful, he represents the work of the old and new covenant in our lives. The Old working death in us in order that we might be raised to life in the new