Neither, because they are the seed of Abraham, [are they] all children: (4) but, In (i) Isaac shall thy seed be called.
(4) The first proof is taken from the example of Abraham's own house, in which Isaac only was considered the son, and that by God's ordinance: although Ishmael also was born of Abraham, and circumcised before Isaac.
(i) Isaac will be your true and natural son, and therefore heir of the blessing.