God did well in giving the promise so many years before the Law, that it may never be said that righteousness is granted through the Law and not through the promise. If God had meant for us to be justified by the Law, He would have given the Law four hundred and thirty years before the promise, at least He would have given the Law at the same time He gave the promise. But He never breathed a word about the Law until four hundred years after. The promise is therefore better than the Law. The Law does not cancel the promise, but faith in the promised Christ cancels the Law.
The Apostle is careful to mention the exact number of four hundred and thirty years. The wide divergence in the time between the promise and the Law helps to clinch Paul's argument that righteousness is not obtained by the Law.
Let me illustrate. A man of great wealth adopts a strange lad for his son. Remember, he does not owe the lad anything. In due time he appoints the lad heir to his entire fortune. Several years later the old man asks the lad to do something for him. And the young lad does it. Can the lad then go around and say that he deserved the inheritance by his obedience to the old man's request? How can anybody say that righteousness is obtained by obedience to the Law when the Law was given four hundred and thirty years after God's promise of the blessing?
One thing is certain, Abraham was never justified by the Law, for the simple reason that the Law was not in his day. If the Law was non-existent how could Abraham obtain righteousness by the Law? Abraham had nothing else to go by but the promise. This promise he believed and that was counted unto him for righteousness. If the father obtained righteousness through faith, the children get it the same way.
We use the argument of time also. We say our sins were taken away by the death of Christ fifteen hundred years ago, long before there were any religious orders, canons, or rules of penance, merits, etc. What did people do about their sins before these new inventions were hatched up?
Paul finds his arguments for the righteousness of faith everywhere. Even the element of time serves to build his case against the false apostles. Let us fortify our conscience with similar arguments. They help us in the trials of our faith. They turn our attention from the Law to the promises, from sin to righteousness; from death to life.
It is not for nothing that Paul bears down on this argument. He foresaw this confusion of the promise and the Law creeping into the Church. Accustom yourself to separate Law and Gospel even in regard to time. When the Law comes to pay your conscience a visit, say: "Mister Law, you come too soon. The four hundred and thirty years aren't up yet. When they are up, you come again. Won't you?"
VERSE 18. For if the inheritance be of the law, it is no more of promise.
In Romans 4:14, the Apostle writes: "For if they which are made of the law be heirs, faith is made void, and the promise made of none effect." It cannot be otherwise. That the Law is something entirely different from the promise is plain. The Law thunders: "Thou shalt, thou shalt not." The promise of the "seed" pleads: "Take this gift of God." If the inheritance of the gifts of God were obtained by the Law, God would be a liar. We would have the right to ask Him: "Why did you make this promise in the first place: 'In thy seed shall all the nations of the earth be blessed'? Why did you not say: 'In thy works thou shalt be blessed'?"
VERSE 18. But God gave it to Abraham by promise.