But he who was of the bondwoman,.... Ishmael, who was begotten and born of Hagar,was born after the flesh; after the common order and course of nature, through the copulation of two persons, the one able to procreate, and the other fit for the conception of children; and was typical of the Jews, the natural descendants of Abraham, who, as such, and upon that account, were not the children of God, nor heirs of the eternal inheritance:but he of the free woman was by promise; by a previous promise made by God to Abraham, that he should have a son in his old age, when his body was now dead, and when Sarah his wife, who had always been barren, was now grown old, and past the time of bearing children; so that Isaac was born out of the common order and course of nature; his conception and birth were owing to the promise and power of God, and to his free grace and favour to Abraham.
This son of promise was a type of the spiritual seed of Abraham, whether Jews or Gentiles, the children of the promise that are counted for the seed; who are born again of the will, power, and grace of God, and are heirs, according to the promise, both of grace and glory, when they that are of the law, and the works of it, are not.