Romans 4:18

Who in hope believe against hope, to the end that he might become a father of many nations, according to that which had been spoken, So shall thy seed be. [Now, since a righteousness of law is unattainable by men, the inheritance was bestowed because of a righteousness of faith, that it might be a free gift, and that all the promises concerning it might be sure, to the entire household. Not only to that division of Abraham's spiritual children who are under the law (believing Jews), but also to that part who are only his children by reason of a like faith with him (believing Gentiles), for Abraham is the father of all believers, whether Jews or Gentiles; as it is written, "A father of many nations have I made thee." And Abraham was such a spiritual father in the estimate of God, who, in his omnipotence and omniscience, gives life to the dead (and, from a child-bearing standpoint, Abraham and Sarah were as good as dead), and speaks of unborn and as yet non-existent children as though they already had being. And God spoke thus to the man who, when nature withheld all reason to hope, still hoped for the purpose of obtaining from God the fulfillment of the promise that he should be the father of many nations, according to God's gracious assurance, when he bade Abraham look upon the stars, and said, "So shall thy seed be." The word "made," in Romans 4:17; means to constitute or appoint. "This word," says Shedd, "denotes that the paternity spoken of was the result of a special arrangement or economy. It would not be used to denote the merely physical connection between father and son." Such a word is to be expected, for the promise was that Abraham was to be a spiritual, not a fleshly, father of many nations. Again, it is fittingly said that Abraham was such in God's sight, for it was God, and not man, who thus anticipated the future. Though Abraham and Sarah were long past the age of child-bearing, and though it was to be many centuries before Abraham would have spiritual children, begotten of the gospel among the Gentiles, yet God spoke of him as the father of many nations; foreknowing his own power and foreseeing his own workings, God meant both to make him a father in the near future, and to give him a spiritual seed among the Gentiles in the remote future.]