Galatians 4:26-28

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] And we, [believing] brothers and sisters, like Isaac, are children [not merely of physical descent, like Ishmael, but are children born] of promise [born miraculously].