John Calvin Commentary Romans 4:14

"For if they that are of the law are heirs, faith is made void, and the promise is made of none effect:" — Romans 4:14 (ASV)

For if they who are of the law, etc. He takes his argument from what is impossible or absurd: that the favor Abraham obtained from God was not promised to him through any legal agreement or regard to works. For if this condition had been introduced—that God would favor with adoption only those who deserved it or who performed the law—no one could have dared to feel confident that it belonged to him. Who is there so conscious of such perfection that he can feel assured the inheritance is due to him through the righteousness of the law?

Then faith would be made void, because an impossible condition would not only hold people's minds in suspense and anxiety but also fill them with fear and trembling. Thus, the fulfillment of the promises would be rendered void, for they accomplish nothing unless received by faith. If our adversaries had ears to hear this one reason, the contest between us might easily be settled.

The Apostle assumes it as an undoubted truth that the promises would by no means be effective unless they were received with full assurance of mind. But what would be the case if people's salvation was based on keeping the law? Consciences would have no certainty but would be harassed with perpetual restlessness and eventually sink in despair.

The promise itself, whose fulfillment depended on what is impossible, would also vanish without producing any fruit. Away then with those who teach the common people to seek salvation for themselves by works, since Paul expressly declares that the promise is abolished if we depend on works.

But it is especially necessary that this should be known—that when there is a reliance on works, faith is reduced to nothing. From this we also learn what faith is, and what the righteousness that comes from works ought to be, in which people may safely trust.

The Apostle teaches us that faith perishes unless the soul rests on the goodness of God. Faith, then, is not mere knowledge of God or His truth, nor is it a simple persuasion that God exists and that His word is the truth. Instead, it is a sure knowledge of God’s mercy, received from the gospel, which brings peace of conscience with regard to God and rest to the mind.

The sum of the matter then is this—that if salvation depends on keeping the law, the soul can entertain no confidence concerning it; indeed, all the promises God offers us will become void. We must thus become wretched and lost if we are sent back to works to find the cause or the certainty of salvation.