Galatians 4:26-27

But the Jerusalem above [that is, the way of faith, represented by Sarah] is free; she is our mother. For it is written [in the Scriptures], “REJOICE, O BARREN WOMAN WHO HAS NOT GIVEN BIRTH; BREAK FORTH INTO A [joyful] SHOUT, YOU WHO ARE NOT IN LABOR; FOR THE DESOLATE WOMAN HAS MANY MORE CHILDREN THAN SHE WHO HAS A HUSBAND.” [Is 54:1]