Abram and Sarah had lived together for many years during which time they worked as a team, as partners, as equals, as leaders realizing an ideal to which they were committed.
When the turning point came, a new relationship was formed between them.
They underwent a name change, becoming Abraham and Sarah, as an indication of rebirth.
Abraham was circumcised; Sarah entered the female cycle once again.
This transformation provides the symbolic meaning of the story of the patriarchs,
In earlier generations, to the extent that it existed at all, spiritual influence passed from teacher to pupil.
Here, this spiritual tie received a new dimension and was reinforced by the biological tie, by the birth of the child who would transmit the ideal throughout the generations of his descendants.
For this reason, Abraham and Sarah were not only the spiritual forebears of the Jewish people.
The meaning of the name "Children of Israel" could be made tangible only when the relationship between them underwent another level of change and became a blood tie, a biological link.
It thus became the relationship that bore Isaac, in order that he, and only he, could continue the line arising from the union of Abraham and Sarah to form the nation of Israel, the Jewish people.
This biological-spiritual relationship has withstood the test of time, throughout the generations that followed.
The converts of Abraham and Sarah have disappeared into history, and what has remained is the product of the strength and validity of that double bond: the Jewish nation.
The dual parenthood of Abraham and Sarah remained, but only when Sarah gave birth to a child from her own womb -"Sarah thy wife shall bear thee a son indeed" (Genesis17:19) -could they become the eternal parents of Israel in the fullest sense.
–Rabbi Adin Steinsaltz
From Biblical Images by Rabbi Adin Steinsaltz