Most studies of the Republic of Vietnam’s nation building programs have focused on its security and economic dimensions. Yet spirituality was a fundamental element of Ngô Đình Diệm’s Personalist Revolution. This article analyzes how the Republic of Vietnam attempted to channel the religious nationalism emerging from the First Indochina War. The spiritual dimension of the Republic’s Personalist Revolution did not involve State interference in all religious activities. Instead, it promoted religious freedom and diversity, provided that the spiritual values they propagated, opposed Communism’s atheism. In practice, this framework did not succeed in creating a religious alliance against Communism. In fact, it strengthened a religious consciousness which would increasingly challenge the State, its assumption that religions opposed Communism, and the very principle of religious diversity.