Romans 4:16

For this cause it is of faith, that it may be according to grace; to the end that the promise may be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham, who is the father of us all.

For four definitions of "seed," see under Romans 4:13. If only the literal seed of Abraham were to be heirs, and only the legal portion of that, called the legal seed, the spiritual seed would be disinherited.

According to grace ... The most basic thing of all, regarding the salvation which Almighty God has provided for his erring human children, is the fact of its derivation, in the last analysis, from the unmerited favor bestowed upon them by the heavenly Father. Look: when the angels sinned, no salvation was provided for them; and God certainly did not owe salvation to people; and it was contrary to all precedent that any was provided. The fact that people, as such, cannot merit this generous treatment at the hands of God is absolutely axiomatic. Of course, they cannot. Therefore, what an incongruous thing it would have been if the blessed Messiah himself should have been through such a device as the law of Moses, especially since that law was only a temporary device anyway, and applied to a tiny fraction of earth's populations, and not even they kept it! Therefore the promise was made to Abraham upon the premise of his obedient faith, a faith which God repeatedly tested and proved, even to the extent of requiring the offering up of Isaac. Abraham obeyed! Abraham's obedience is not emphasized in this chapter, although stated clearly enough; but it is most certainly a part of the total picture. The reason that Paul did not stress obedience here lies in the fact that even Abraham's obedience was not perfect, as, for example, in the matter of taking Terah with him; therefore, his obedience in any perfect sense could not have been made the ground of God's promise; but his obedience was indeed sufficient to exhibit and prove his faith. Despite that, Paul was correct in leaving obedience in the background in this chapter. That obedience was not excluded from the definition of Abraham's faith as the ground of his justification is implicit in two things: (1) Paul did not say that it was Abraham's faith alone. The commentators certainly have no trouble finding that word, their exegesis being filled with it from one end to the other, which only points up the significance of the fact that never, not even once, did Paul use such an expression as "faith only" or "faith alone." We are absolutely safe, therefore, in the conviction that Paul designedly avoided such, and it is equally certain that the quality of Abraham's obedience entered into and formed a part of the consideration on God's part when Abraham was selected to be the "father of the faithful." (2) The second consideration is this: The obedient nature of Abraham's faith appears in the twelfth verse where those who shall inherit are described as those who will "walk in the steps of" Abraham's faith, the same being an inspired statement that would have been impossible to make without considering the "faith" so frequently mentioned in this chapter to have been an "obedient faith."

(The seed) ... which is the law ... is a reference to those faithful Jews who believed God, walking in all the commandments and ordinances of the Lord, such as Zacharias, and countless others of the old institution, who also are part of the extended spiritual seed which includes many nations, peoples, and tongues. Paul was careful to make it plain that no Israelite was excluded from the promise; for they also would inherit through obedient faith.