That is the new Michael Walzer book, with the subtitle Secular Revolutions and Religious Counterrevolutions. The stated paradox is fairly simple, yet worthy of sustained attention:
Why have the leaders and militants of secular liberation not been able to consolidate their achievement and reproduce themselves in successive generations? Over the past several decades, Indian intellectuals and academics have been debating this question in its local version: “Why is it,” one of them asks, “that the Nehruvian vision of a secular India failed to take hold?”
Other cases considered include Israel, Palestine, and Algeria, as well as the Middle East more generally. Walzer doesn’t much try to answer his own question, but this book is very stimulating and worth the short amount of time it takes to read it. I would modify the paradox however: I see various European nations which do consolidate and maintain largely secular nationalist movements. How about Denmark or France? If you find those examples troublesome, try Serbia or for that Vietnam or China. There may be a more general issue of morphing, above and beyond the religious vs. secular issue.