This thesis seeks to understand the rationale for membership in the Zion community envisaged by Isaiah 56-66. Previous scholarship has produced no holistic consideration for the use of the Abrahamic and Sinaitic covenants in the depiction of Zion's establishment. Part One of this thesis investigates the Zion community and its membership rationale, Abrahamic and Sinaitic covenantal roots, and Zion's establishment as Yahweh's community in the Core (Is. 60:1-62:12). Part Two shows how the rationale is applied to membership, i.e., to both inclusions and exclusions in the Framework sections (Is. 56-57; 65-66). Select exegesis of the Core shows the establishment of the Zion community (Ch. 1), then allusions in the Core to the earlier Abrahamic and Sinaitic covenants are used to compare the establishment of Zion with that of Abraham and Israel respectively (Chs. 2-3). Finally exegesis of the Framework sections demonstrates application of the rationale for inclusions in and exclusions from the community (Chs. 4-6). The covenantal nature of Zion's establishment is the key to her membership; its granting is seen in the promise of inclusions and its withdrawal in the threats of exclusions. Allegiance to Yahweh and holiness constitute the rationale for membership.