2. The numerous natural posterity promised to Abraham was also a type of the spiritual seed, the true members of the church of Christ, springing from the Messiah, of whom Isaac was the symbol. Thus St. Paul expressly distinguishes between the fleshly and the spiritual seed of Abraham; to the latter of which, in their ultimate and highest sense, the promises of increase as the stars of heaven, and the sands of the sea shore, are to be referred, as also the promise of the heavenly Canaan.
3. The intentional offering up Isaac, with its result, was probably that transaction in which Abraham, more clearly than in any other, “saw the day of Christ, and was glad.” He received Isaac from the dead, says St. Paul, “in a figure.” This could be a figure of nothing but the resurrection of our Lord; and, if so, Isaac’s being laid upon the altar was a figure of his sacrificial death, scenically and most impressively represented to Abraham. The _place_, the same ridge of hills on which our Lord was crucified; the _person_, an only son, to die for no offence of his own; the _sacrificer_, a father; the _receiving back_, as it were, from death to life; the _name_ impressed upon the place, importing, “_the Lord will provide_,” in allusion to Abraham’s own words to Isaac, “the Lord will provide a lamb for a burnt offering;” all indicate a mystery which lay deep beneath this transaction, and which Abraham, as the reward of his obedience, was permitted to behold. “The day” of Christ’s humiliation and exaltation was thus opened to him; and served to keep the great truth in mind, that the true burnt offering and sacrifice for sin was to be something higher than the immolation of lambs and bulls and goats,--nay, something more than what was _merely_ human.
4. The transaction of the expulsion of Hagar was also a type. It was an allegory in action, by which St. Paul teaches us to understand that the son of the bondwoman represented those who are under the law; and the child of the freewoman those who by faith in Christ are supernaturally begotten into the family of God. The bondwoman and her son being cast out, represented also the expulsion of the unbelieving Jews from the church of God, which was to be composed of true believers of all nations, all of whom, whether Jews or Gentiles, were to become “fellow heirs.”