Even though this was very OffTopic, it remembered me of an InternationalObfuscatedCeeCodeContest entry:
The entry of phillips in the year 1988, which compressed the song into a C program:

http://ioccc.org/years.html#1988

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There may be one Christmas Carol that has always baffled you. What in the world do leaping lords, French hens, swimming swans, and especially the partridge who won't come our of the pear tree have to do with Christmas? 

From 1558 until 1829, Roman Catholics in England were not permitted to practice their faith openly. Someone during that era wrote this carol as a catechism song for young Catholics. It has two levels of meaning: the surface meaning plus a hidden meaning known only to members of their church. Each element in the carol has a code word for a religious reality which the children could remember. 

	1 The partridge in a pear tree was Jesus Christ (crucified on a cross/tree).
	1 Two turtle doves were the Old and New Testaments.
	1 Three French hens stood for faith, hope and love. 
	1 The four calling birds were the four gospels of Matthew, Mark, Luke & John. (colley birds in the original)
	1 The five golden rings recalled the Torah or Law, the first five books of the Old Testament. (ie: Genesis, Exodus, Leviticus, Numbers, Deuteronomy)
	1 The six geese a-laying stood for the six days of creation. 
	1 Seven swans a-swimming represented the sevenfold gifts of the Holy Spirit - Prophesy, Serving, Teaching, Exhortation, Contribution, Leadership, and Mercy. 
	1 The eight maids a-milking were the eight beatitudes. (Matthew 5:3-9)
	1 Nine ladies dancing were the nine fruits of the Holy Spirit - Love, Joy, Peace, Patience, Kindness, Goodness, Faithfulness, Gentleness, and Self Control. (Galatians 5:22-23)
	1 The ten lords a-leaping were the ten commandments. (Exodus 20:1-17)
	1 The eleven pipers piping stood for the eleven faithful disciples. (Matthew 10:2-4)
	1 The twelve drummers drumming symbolized the twelve points of belief in the Apostles' Creed. 

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Hmmm. This sounds to me a bit like an after-the-fact invention. Evidence please? (saying "I heard it on the BBC" doesn't count.)

This derivation is discussed on http://www.cresourcei.org/cy12days.html

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See ''The Twelve Days of Christmas'' in the Urban Legends Reference Pages (http://www.snopes.com/holidays/christmas/music/12days.asp) for why the "coded reference" theory does not stand:

	 :	The key flaw [...] is that the differences between the Anglican and Catholic churches were largely differences in emphasis and form which were extrinsic to scripture. [...] All of the religious tenets supposedly preserved by the song "The Twelve Days of Christmas" (with the possible exception of the number of sacraments) were shared by Catholics and Anglicans alike: both groups' bibles included the Old and New Testaments, both contained the five books that form the Pentateuch, both had the Four Gospels, both included God's creation of the universe in six days as described in Genesis, and both enumerated the Ten Commandments. [...] None of these items would distinguish a Catholic from a Protestant, and therefore none of them needed to be "secretly" encoded into song lest their mention betray one as a Catholic. [...] Conversely, none of the important differences that would obviously distinguish a Catholic from a Protestant is mentioned here. A Catholic would have good reason not to possess or reveal anything that would indicate his allegiance to the Pope or his participation in the sacrament of penance (also known as Confession), but nothing of that nature is encapsulated in the explanation of the symbolism supposedly to be found in the "The Twelve Days of Christmas." 

''It's all part of a complex plot to make you use Bing.''