He begins with the ideas of the ancient Greeks ("Athens" serves as a synecdoche for the Greek rational tradition) and the Judeo-Christian ideas (represented by "Jerusalem"). The fusion of the two produced the Western world and ultimately the United States. Correlatively, it produced unprecedented progress, well-being and human flourishing.
There's nothing new in this analysis, of course, but unfortunately each generation, especially today's millennials, needs to be reminded of this history and the source of the manifold blessings they enjoy as beneficiaries of this tradition.
Shapiro's main thesis is that Western culture went off the rails when the Enlightenment thinkers split Athens off from Jerusalem, clinging to the former and rejecting the latter. This was especially so in the case of the French Enlightenment which subsequently spawned the horrors of the French terror and contributed to the evolution of modern leftism and its postmodern variants, together with its totalitarian predilections.
As Shapiro states, "Lasting happiness can only be achieved through the cultivation of soul and mind. And cultivating our souls and minds requires us to live with moral purpose."
Enlightenment thinkers, in their hubris, believed they could dispense with the moral and epistemological foundations provided by Jerusalem's God and still harvest all the fruits of Athenian reason, but this project has culminated in the postmodern scuttling of both Jerusalem and Athens. Here's Shapiro explaining the postmodern disdain for reason:
Reason, in fact, is insulting. Reason suggests that one person can know better than another, that one person's perspective can be more correct than someone else's. Reason is intolerant. Reason demands standards. Better to destroy reason than to abide by its dictates.Tragically, the postmodern rejection of both Jerusalem and Athens has left contemporary Westerners metaphysically empty and void of the kinds of resources needed to satisfy their deepest psycho-emotional yearnings and appetites.
The Greeks thought that men had a purpose, a telos, the striving for which gave their lives meaning, but in a world bereft of God there is no "moral purpose." The Enlightenment, and later Darwinism, made God superfluous and consequently made the idea of a telos untenable. There can be no purpose for humanity if man and the cosmos are all simply freak accidents, and if there is no God then everything is nothing more than a meaningless, ephemeral flux of atoms.
The New Left emerged from the social thought of philosopher Herbert Marcuse (1898-1979) who rejected toleration of speech and ideas promoted by those who oppose the New Left's agenda. He held that freedom as it had been traditionally understood simply served the cause of oppression, that speech could be labelled violence, and that minority groups should be given special privileges including the right to shut down their opposition.
These ideas paved the way for the sexual revolution, victim politics, political correctness, and eventually, intersectionality.
Shapiro crams all this into about 250 pages, and, if you like reading about ideas and their real-world consequences, it's all really quite interesting.