The historical extent of Judaism depends on how we understand Abraham and Sarah, the best candidates for the title "progenitors," and where we place them chronologically. If we assume that they were historical figures, rather than literary constructs, we talk about the beginning of a people, a line of blood and culture. The most probable date for the first generations of that people, who become self-conscious as tribes derived from Jacob ("Israel"), the grandson of Abraham and Sarah, is the (Middle Bronze) period ( 2000-1500 B.C.E). Archaeological research suggests that the customs described in the cycle of stories about Abraham and Sarah in Genesis appear about that time. Later (perhaps 1200 B.C.E.) comes the exodus from Egypt under Moses, and later still comes the reign of King David (ca. 1013-9 73) B.C.E.).
Because of Genesis we associate Abraham and Sarah with the experience of faith in an other-worldly, truly unique God. The stories about Abraham stress his difference from his idolatrous father. They also stress the promise of the living, uncapturable God that Sarah and Abraham will become the font of a vast progeny, like the stars in the heavens or the grains of sand along the beach. This is mystical but probably only in the sense that all religious faith is a response to the mystery of God, a mode of access to the unknowable primacy of the divine and a mode of suffering from that primacy.