The holy Apostle did lay as the foundation of this statement that where there is no law, there is no transgression. Or he taught that transgression is bound to the law, whether the law merely gives occasion to it or directly causes it. He thereby lets us understand that where there is transgression, there is wrath.
Yet even this, that the law gives occasion to transgression or leads to it, is not entirely clear. For the law was given so that all might see how they must act, act righteously, and therefore be free from transgression. It was not given in order to introduce them into transgression.
Saint Paul resolves this difficulty below, saying that the cause is not the law, but our weakness. The law in itself is holy, and the commandment holy, righteous, and good. But I am sold under sin. Sin dwells in me and draws me toward lawlessness.
I see what the law requires, and I rush to fulfill it. But sinful arousal comes and draws me into transgression of the law. Thus the law is a poor helper to me. It only exposes my sinfulness and transgression more brightly.
If I did not know the law, then although I sinned, my sins would be sins of ignorance. But here you see and still sin. And if this happened only once or twice a month or week, it would be tolerable. But it happens every day and hour. Rarely does anything pass without crookedness.
It turns out that the law only covers you with sins, so that you do not know where to flee from them or how to cast off their oppressive burden. “O wretched man that I am! Who will deliver me?” (cf. Rom 7:24).
But what is to be done? This would indeed be the case if God had left us forever with the law alone. Man would sink deeper and deeper into the consciousness of his sinfulness, and therefore into the feeling of being under God’s wrath. Nothing more. He would find no means in the law to set matters right.
This awareness of the hopelessness of one’s condition under the law alone is what the Apostle has in mind whenever he reasons about the relation of law and faith. He has the same intention here. He speaks as though saying: remain with the law alone, and you will remain entirely in sinfulness and under wrath.
Through this you cut off the blessing and do not allow Abraham’s promise to be fulfilled in you. You destroy this promise. Do you wish the promise given to Abraham to be fulfilled in you? Receive faith.
The promise was given to faith, and under the condition of faith it is brought to fulfillment. Faith brings forgiveness of transgressions committed in relation to the law. It gives strength to fulfill the law, and so brings one into righteousness, upon which blessing rests. In this way the promise is fulfilled.