In his autobiography Il pellegrino di Roma ("The Pilgrim from Rome", 1945), Buonaiuti reconstructed the history of his conflict with the Catholic Church, of which he continued to claim himself a "loyal son", even after his excommunication.
[4] The complete works of Buonaiuti are very extensive: he wrote more than three thousand works, including books and articles, among them the ponderous Storia del Cristianesimo ("History of Christianity") in three volumes, his autobiography (Il pellegrino di Roma) and many studies about Gioacchino da Fiore (Gioacchino da Fiore: i tempi, la vita, il messaggio) and Martin Luther (Lutero e la riforma in Germania).
Christianity, born as an announcement of palingenesis, implied a huge social program "which imposed a progressive conceptual enrichment and an increasingly rigid disciplinary organization.
The only chance of salvation for the Church and all of modern society is, in Buonaiuti's view, the restoration of the elementary values of primitive Christianity: love, pain, regret, death.
Buonaiuti claimed to be Catholic and to want to stay so usque dum vivam ("as long as I live"), as he wrote to the theology faculty of the University of Lausanne, which had offered him a chair in History of Christianity if he joined the Calvinist Church.
[6] Ricky Tognazzi's 2003 film The Good Pope has a character called Nicola Catania who is loosely based on Buonaiuti, although a certain amount of licence is employed.
The movie has Catania, a priest deposed for Modernism, keeping vigil in St. Peter's Square as John XXIII, who had been his friend in the seminary lies dying.