Not only does the law inevitably bring a curse, but justification cannot be by the law because the only way to be justified according to Scripture is by faith. This, Paul says, is evident; it is obvious, and to prove it, he quotes Habakkuk 2:4.
How can a human being be counted just before God unless he has a righteousness which is acceptable to the infinitely holy God? Therefore God himself must provide that righteousness, for only he has a righteousness that meets his own exacting standards. Where does the righteousness that God imputes to us come from? It is the righteousness of the only one who has ever lived without sin, who has obeyed the law perfectly, the righteousness of Christ who came to fulfil the law in our place. While we are justified by faith, he was born under the law and was not released until he had fulfilled it in every respect. His success in doing so allows him to credit us with his own righteousness. Christ justifies us by taking away our sin and suffering the eternal consequences of it under the law, and by giving us a perfect righteousness which makes us fit for heaven.