E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The case is altered. quoth Plowden. Plowden was a priest, very unpopular, and in order to bring him into trouble some men inveigled him into attending mass performed by a layman, and then impeached him for so doing. Being brought before the tribunal, the cunning priest asked the layman if it was he who officiated. Yes, said the man. And are you a priest? said Plowden. No, said the man. Then, said Plowden, turning to the tribunal, that alters the case, for it is an axiom with the church, No priest, no mass.