Romans 4:16

Therefore it is of faith, that it might be by grace - On this account the promise is mercifully grounded, not on obedience to a law, but on the infinite goodness of God: and thus the promise is sure to all the seed - to all, both Jews and Gentiles, who, believing in Christ Jesus, have a right to all the blessings contained in the Abrahamic covenant. All the seed necessarily comprehends all mankind. Of the Gentiles there can be no doubt, for the promise was given to Abraham while he was a Gentile; and the salvation of the Jews may be inferred, because they all sprang from him after he became an heir of the righteousness or justification which is received by faith; for he is the father of us all, both Jews and Gentiles. Dr. Taylor has an excellent note on this verse. "Here," says he, "it should be well observed that faith and grace do mutually and necessarily infer each other. For the grace and favor of God, in its own nature, requires faith in us; and faith on our part, in its own nature, supposes the grace or favor of God. If any blessing is the gift of God, in order to influence our temper and behavior, then, in the very nature of things, it is necessary that we be sensible of this blessing, and persuaded of the grace of God that bestows it; otherwise it is not possible we should improve it. On the other hand, if faith in the goodness of God, with regard to any blessing, is the principle of our religious hopes and action, then it follows that the blessing is not due in strict justice, nor on the foot of law, but that it is the free gift of Divine goodness. If the promise to Abraham and his seed be of faith on their part, then it is of grace on the part of God. And it is of faith, that it might be by grace: grace, being the mere good will of the donor, is free and open to all whom he chooses to make the objects of it: and the Divine wisdom appointed faith to be the condition of the promise; because faith is, on our part, the most simple principle, bearing an exact correspondence to grace, and reaching as far as that can extend; that so the happy effects of the promise might extend far and wide, take in the largest compass, and be confined to no condition, but what is merely necessary in the nature of things."