During the brit mila, it is customary to reserve a seat for the prophet Eliyahu, who comes to every brit mila. Eliayhu was an extremely zealot in honoring Hashem. He said to Hashem, disapprovingly of Bnai Israel, “The Bnai Israel have forsaken Your covenant” (Melachim 19:10). During the period of the wicked king Achav, the Jews were forbidden to perform brit mila. For that reason, Hashem gave Eliayhu the privilege to be a witness at every brit mila thereafter, thereby seeing the continuation of the Jewish people.