Just a brief quote and a few quick comments:
The principal affirmation is that law and religion are two different but interrelated aspects, two dimensions of social experience--in all societies, but especially in Western society, and still more especially in American society today . Despite the tensions between them, one cannot flourish without the other. Law without (what I call) religion degenerates into a mechanical legalism. Religion without (what I call) law loses its social effectiveness. [Italics added]
Indeed. Law is a necessary and inescapable part of life in this world. Civilization cannot function without it. For Christians to ignore or deny God's law and its ongoing applications both for the individual as well as for society at large is to consign the Christian faith to irrelevance--or in Berman's words, the Christian faith will "lose its social relevance."
Worse, for Christians to deny God's law is to (unwittingly) advocate for the worship of another god in the public square. As Rushdoony said, "It must be recognized that in any culture the source of law is the god of that society" (Institutes of Biblical Law, p. 4). It may not be a traditionally recognized deity, whether the One and Only True God of the Bible or any one of a number of false gods (Baal, Chemosh, Vishnu, Zeus, etc.), but whatever is held to be the source or origin of law (nature, reason, experience, etc.) has for all practical assumed the role of divinity.
If this is true, are we really preaching the gospel if we omit the comprehensive claims of the Christian faith?