Romans 9:6-8

Mace(i) 6 However, the divine promise cannot but have its effect. for they are not the whole of Israel, who are descended from Israel: 7 neither are they who are the race of Abraham, all children: but 'tis said, "in Isaac shall thy posterity be called." 8 that is, the children by natural descent are not thereby the children of God: but the children of the promise are alone considered as his posterity.