"And God said to Abraham... 'whatever Sarah tells you, heed her voice, since through Isaac will offspring be considered yours'" Genesis 21:12
Perhaps the most difficult test faced by our forefather Abraham was when Sarah asked him to banish his son Ishmael from their home. Abraham was the pillar of love and kindness in the world; to banish his own son from his home was anathema. But God supported Sarah's motherly instincts and instructed Abraham to heed her decision. Our sages deduced from this that Sarah was superior to Abraham in her capacity to intuit God's will.
Rav Meir Simcha of Dvinsk draws our attention to a remarkable passage in the Talmud. Rebbi Banah visited the burial site of our forefathers and matriarchs, where he witnessed Abraham lying in the arms of Sarah while she was "examining" his head.
According to Rav Simcha, the parable illustrates the fact that the souls of the Jewish people are inextricably bound to each other. An individual soul is incapable of achieving its own perfection without interaction with other souls. Abraham was a spiritual giant but he was not perfect. Sarah had the unique capability to draw on Abraham's spiritual strengths and discard his imperfections.
This ability is symbolised in Sarah's examining Abraham's head. She was choosing which of his attributes would be necessary to establish the next generation of forebears of the Jewish people. When she came across something that could harm their future, she cast it aside. Sarah understood that Hagar's shortcomings would cause Abraham's imperfections to be passed on to Ishmael.
Abraham's capacity to become the forebear of a holy nation could be realised only in partnership with Sarah. Through her keen spiritual powers, ultimately she was able to bring out the best in both of them.