There is more in Israel’s history than the law. Abraham believed God, and it was imputed to him for righteousness. (See Rom. 4:3). He was reckoned righteous because of his faith. Also, David said, ‘Blessed is the man whose iniquity is forgiven, whose sin is covered; blessed the man to whom the Lord imputeth no sin.’ (Psalm 32:2). No sin was imputed to him. He was held to be wholly clear of it before God; it was forgiven and covered. The responsibility of man was fully met, and he knew it.
Faith was counted for righteousness to Abraham. Circumcision was only a seal of the righteousness he had already before he was circumcised. Therefore he became the father of all who believe (including uncircumcised, believing Gentiles), and more than that, the father of those truly separated to God – circumcised in spirit, not in letter.
The promise to Abraham that he would be the heir of the world was a matter of law, but of the righteousness of faith. Promise is not law: promise and faith go together. If promise had been on the basis of law, faith would have been void – man could not have had an inheritance because of transgression. But the inheritance is of faith, not law, that it might be by grace. Faith just believes in grace.
When Abraham received the promise, as far as having offspring was concerned, he was as good as dead. But he believed what God had said as to his seed. So we have another important principle: grace and promise on the part of God, and faith, and the redemption that is in Christ, on the part of man. God’s power comes in; God raises the dead, and makes them to be as He calls them. This applies to Abraham’s seed, to the Gentiles’ blessing, and to Christ’s physical resurrection.
Law requires power in man to fulfill it. The law being given to the sinner, wrath was the consequence of its imposition. A dead person has no power; resurrection is by God’s power, and Abraham believed that. If God spoke, the thing was certain. That is why his faith was imputed to him for righteousness. When man justifies God not himself, God justifies him. Abraham believed that God was able to perform what He had said; we believe that He raised Christ from the dead – delivered for our offences, and raised again for our justification. God glorifies Himself in grace by granting divine righteousness to man, when he had no human righteousness before God.
As to ourselves, righteousness is imputed to us, as we believe on the God who raised up Christ from the dead. We do not merely own Christ’s work, but God’s acceptance of that work, and His power to quicken the dead. As John said, ‘God is able of these stones to raise up children unto Abraham.’ (Matt 3:9). God demonstrated His power in raising up Christ from death, the state into which our sins had brought Him through grace. Of course, God could not leave Him in death, for He was satisfied as to the matter of sins, and righteously raised Him from the dead – in public testimony.
A simplified summary of part of the introduction to John Nelson Darby’s Exposition of the Epistle to the Romans