a late middle English translation and expansion is here). My own modernization [FN2] of the expanded Middle English version follows:
Of the Parson that said a Requiem Mass for Christ's Soul
There was a certain country priest that was not especially well educated. Therefore, on the evening before Easter he sent his boy to the priest of the next town (about two miles from him) to know what mass he should sing the next day. This boy came to the neighboring priest and made his master's request.
The neighboring priest then responded, "Tell your master that he must sing tomorrow of the resurrection." The priest further added, "if you happen to forget it, tell your master that it begins with a capital 'R'," and showed him the mass book where it was written "Resurrexi." etc.
The boy then went home again, and all the way as he went he kept repeating "Resurrexi Resurrexi." At the last minute, however, it happened to fall clean out of his mind. When he came home, his master asked him what mass he should sing tomorrow.
"I swear, master," said the boy, "I have forgotten it, but he told me to tell you it begins with a capital 'R'."
"Aha," said the priest, "I know you say the truth, for now I remember well it must be 'requiem eternam,' for god almighty died as though on yesterday and now we must say mass for his soul."
By this you may see that when one fool sends another fool on his errand, oftentimes the business receives fool's-gold help.[FN3]
The moral I'd like to suggest is a little different. I'd like to suggest that an important lesson for us to learn is that we should be careful about using imprecise theological statements. While there is an orthodox sense to the expression that the priest used to describe the Good Friday commemoration of Christ's death, since Christ (who is God) died that day, nevertheless much absurdity can arise (and this story is but one facetious example) from a failure to properly distinguish between those things that belong properly to Christ's human nature (such as to be born, to grow, to learn, to die, and to be raised again) and those that properly belong to Christ's divine nature (such as to be omniscient, eternal, and immutable).
Therefore, we ought to be careful to avoid unnecessary ambiguity in our language. By speaking precisely we may aid the simple and edify the learned.
FN1: This story brought to my attention via Matthew at Shrine of the Holy Whapping
FN2: I've updated not only the spellings of words, and archaic words ("quoth" and "trow" for example) but also the archaic syntax and an instance of the priest taking the LORD's name in vain (replaced by "Aha").
FN3: The original punchline is a little hard to convey. The original ending was "the business is foolishly speed" which makes no sense to the modern reader given the modern shift in the semantic domain of the word "speed." English retains this kind of sense in the word "godspeed" of which "foolspeed" would be a sort of opposite. While we could say "assisted as though by a fool" that would reduce a lot of the punch of the punchline, so I've tried to get as close as possible with "fool's gold help" which manages to include a play on the word "fool" without simply stating the obvious.