In "God's Word for Today" William Snider writes:
Paul's emphasis on the redeeming work of Christ flows out of his intense burden for the Jewish people. Reflecting upon his own background as a Pharisee, he could appreciate that they were zealous for what they understood to be God's purpose and method, but they had misunderstood and twisted the plan to emphasize the human rather than the divine. Their insistence upon the obedience to the law had, in fact, revealed their impotence to keep the law. Yet they had wrapped themselves in self-righteous robes and pronounced themselves acceptable to God. The result was an ethical (and racial) arrogance. The true salvation process is to admit sin and come to Jesus for divine forgiveness. It is a purposeful acknowledgment of Christ as the sole source of salvation and faith in His death to accomplish this purpose. For the Jew, this was to reject their system of religion which had major implications for past and present. Accepting Christ for salvation is no less radical now.
Source: Studies in Romans: Adult Teacher's Insights, page 58-59.