To the end that the promise might be sure to all the seed. – Romans 4:16

Look at this, dear Friends, very carefully. Salvation was made to be of faith and not of works that the promise might be sure to all the seed, for first, it could not have been sure to us Gentiles by the Law, because in a certain sense we were not under the Law of Moses at all. Turn to the text and you find that it runs thus— “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.” That is to say, the Jew, receiving the seal of circumcision and coming under the ceremonial Law, eating its Passover and presenting its sacrifices, might possibly have been reached by a legal method. But we who are Gentiles would have been altogether shut out. As to the Covenant according to the flesh, we are aliens and have never come under its bonds or participated in its privileges and, therefore, Grace chooses to bless us by faith in order that the Gentile may partake of the blessing of the Covenant as well as the Jew.

But there is a still wider reason—it is of faith because the other method has failed, already, in every case. We have all broken the Law and so have put ourselves beyond the power of ever receiving blessing as a reward of merit. Failure at the outset has ruined our future prospects—and from now on—by the deeds of the Law shall no flesh be justified. If your standing depends upon your own works, you are not safe and can never be safe till you are out of this present life, for you might sin and that one offense against the conditions would destroy the Covenant! What remains, then, if we are to be saved at all, but that it should be of faith? This door, alone, is open! Let us bless God that no man can shut it!

How Is Salvation Received? by C. H. Spurgeon

Therefore it is of faith, that it might be by grace… – Romans 4:16

God has chosen to make salvation by faith, “that it might be by Grace.” Now, dear Friends, the Lord might have willed to make the condition of salvation a mitigated form of works. If He had done so, it would not have been of Grace, for it is a principle which I need not explain now, but a fixed principle, that if the blessing is of Grace, it is no more of works, otherwise Grace is no more Grace. As water and oil will not mix, and as fire and water will not lie down side by side in quiet, so neither will the principle of merit and the principle of free favor. You cannot make a legal work to be a condition of a gracious blessing without at once introducing an alien element and really bringing the soul under the Covenant of Works and so spoiling the whole plan of mercy…His work is all of one piece and that one piece is all Grace!

When we read of Abraham’s life, we see that God called him by an act of Sovereign Grace, made a Covenant with him as an act of Grace and that the promised child was born—not of the power of the flesh, but entirely according to promise. Grace reigns through righteousness unto eternal life in the life of the Patriarch and it is illustrated in a thousand ways whenever we see his faith receiving the promises! The holiness of Abraham, since it arose out of his faith, never leads us to ascribe his blessedness to anything but the Grace of God…I never heard anybody hint that the great Patriarch had reason to glory before God. His name is not “the father of the innocent,” but “the father of the faithful.”

Now, inasmuch as we are saved by faith, every Believer is made to see in himself that, in his own instance, it is by Grace. Believing is such a self-renounciating act that no man who looks for eternal life thereby ever talked about his own merits except to count them but dross and dung…. Those who believe in Justification by Faith are the only persons who can believe in salvation by Grace.

How Is Salvation Received? by C. H. Spurgeon