Mendenhall also addresses the theory behind blood ties and their significance to the concept of a covenant. As stated in the Bible, Abraham, Isaac and Jacob are the ancestors of Israel and because of their shared blood, they consequently form a bond. This blood tie is compared to the tie that is established by a covenant, and implies that without their shared blood, covenants would be the only way to ensure such unification of a religious group. Furthermore, Mendenhall notes two additional theories noting how covenants may have begun with the work of Moses, or are even thought to have been established during a true historical event with a valid setting. Regardless of the theories, the creation of covenants may be a mystery to scholars for centuries to come, however, the use of covenants evidenced throughout the biblical sources is an undeniable fact.