My nephew is staying with us at the moment and is keen to sign the 12 Days of Christmas, up the the appropriate day, to us each morning. In an effort to remember all of the lyrics, as my BBC micro singing version obviously didn't burn it in adequately during my childhood, I looked it up.
The first google hit, which I will not link to as I don't want to increase it's page ranking, was a Christian carols page that claimed religious symbolism to each of the days:
1 True Love refers to God 2 Turtle Doves refers to the Old and New Testaments 3 French Hens refers to Faith, Hope and Charity, the Theological Virtues 4 Calling Birds refers to the Four Gospels and/or the Four Evangelists 5 Golden Rings refers to the first Five Books of the Old Testament, the "Pentateuch", which gives the history of man's fall from grace. 6 Geese A-laying refers to the six days of creation 7 Swans A-swimming refers to the seven gifts of the Holy Spirit, the seven sacraments 8 Maids A-milking refers to the eight beatitudes 9 Ladies Dancing refers to the nine Fruits of the Holy Spirit 10 Lords A-leaping refers to the ten commandments 11 Pipers Piping refers to the eleven faithful apostles 12 Drummers Drumming refers to the twelve points of doctrine in the Apostle's Creed
This all sounds slightly dubious to me. A few hits down the ratings we find the wikipedia page. No more reliable a source but it does include the following text:
"The Oxford Dictionary of Nursery Rhymes indicates there are suggestions that "the gifts have significance, as representing the food or sport for each month of the year. Importance [certainly has] long been attached to the Twelve Days, when, for instance, the weather on each day was carefully observed to see what it would be in the corresponding month of the coming year. Nevertheless, whatever the ultimate origin of the chant, it seems probable [that] the lines that survive today both in England and France are merely an irreligious travesty."
"A bit of modern folklore claims that the song's lyrics were written as a "catechism song" to help young Catholics learn their faith, at a time when practicing Catholicism was discouraged in England (1558 until 1829). There is no substantive primary evidence supporting this claim, and no evidence that the claim is historical, or "anything but a fanciful modern day speculation."
"In fact, variations in lyrics provide evidence against the "catechism song" origin. For example, the four Gospels often are described as the "four calling birds," when in fact the phrase "calling birds" is a modern (probably 20th century) phonetic misunderstanding of "colly birds" (blackbirds).[original research?]"
So, the song is probably irreverent but it's not entirely clear. I'd definitely take any religious claims with a large pinch of salt.
For a more surreal take on it the brilliant 12 Days themed Why Bother? interviews between Peter Cook and Chris Morris, which is a gem of improvised comedy. [It's available on CD and in text form.]