How well we know what a profitable superstition this fable of Christ has been for us and our predecessors.
Did he actually say it?
Referring to Roger Pearse, this quote was sourced from a satirical work of John Bale which was written with a "historical" format entitled 'The Pageant of Popes'.
The earliest known source of this statement is actually a polemical work by the Protestant John Bale, the anti-Catholic Acta Romanorum Pontificum, which was first translated from Latin into English as The Pageant of the Popes in 1574: "For on a time when a cardinall Bembus did move a question out of the Gospell, the Pope gave him a very contemptuous answer saying: All ages can testifie enough how profitable that fable of Christe hath ben to us and our companie." The Pope in this case being Leo X. Later accounts of it exist, as recorded by Vatican Librarian, Cardinal Baronius in the Annales Ecclesiastici (1597) a 12-volume history of the Church.
This disputed quote alleged to have been uttered by Pope Leo X is also said to have been referred from Annales Ecclesiastici written by Caesar Baronius.
At a lavish Good Friday banquet in the Vatican in 1514, and in the company of "seven intimates" (Annales Ecclesiastici, Caesar Baronius, Folio Antwerp, 1597, tome 14), Leo made an amazing announcement that the Church has since tried hard to invalidate. Raising a chalice of wine into the air, Pope Leo toasted: "How well we know what a profitable superstition this fable of Christ has been for us and our predecessors."
However, Baronius’ text which is a history of the church since New Testament stopped recording church history at the year 1198, because Baronius died on 30 June 1607 before he could finish it. The last volume XII which was published in 1607 covered the church years of 1100 to 1193. The year in which the quote was purported to be uttered by Pope Leo is not recorded in Baronius version of Annales Ecclesiastici.
Also other references from the net indicate that the pope's pronouncement is recorded in the diaries and records of both Pietro Cardinal Bembo (Letters and Comments on Pope Leo X, 1842 reprint) and Paolo Cardinal Giovio (De Vita Leonis Decimi, , op. cit.), two associates who were witnesses to it.
However, the actual title of the book " 16 books of letters written in the name of Pope Leo X, dedicated to Pope Paul III " is different from the reference title 'Letters and Comments on Pope Leo X'.