3. The seed is Christ, and Abraham's family is defined by union with Him

From Sovereign Grace and the Scope of Election: A Comparative Examination of Attainment Theology and Grace Theology, with Particular Attention to the Question of Whether God's Elect Are Found Among All Nations and Religions

"Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ" (Galatians 3:16). Every Abrahamic promise funnels through one Person; therefore membership in the promise runs through union with that Person: "Know ye therefore that they which are of faith, the same are the children of Abraham" (3:7); "There is neither Jew nor Greek... for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise" (3:28-29). Paul closes the same letter by naming the church exactly what the attainment system's scheme forbids: "peace be on them, and mercy, and upon the Israel of God" (Galatians 6:16), pronounced over all who walk by the rule of the new creation, uncircumcised Galatians included.