Kedushat Yisrael, the metaphysical distinctiveness of the children of the patriarchs and matriarchs, is a consequence of ancient Israel standing at Sinai, and after hearing the word of God and experiencing revelation, agreeing to accept the responsibilities of being God’s chosen people. This kedusha is given concrete expression in a lifestyle characterized by observing the mitzvot. Kedusha is ever and always defined in proximity to the Holy One. Kedushat Yisrael is transmitted by mother to child because each mother is a child of someone who is of the sacred family of Abraham and Sarah, and thus possesses kedusha. Yisrael is a family that became a faith while remaining a family.
Yehiel E. Poupko, “Making Jews: Conversion and Mitzvot”, Sh’ma (March 2011), 13.