The Law and the Promise

To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified.

This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.

Now this may be interpreted allegorically: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar.