Twelve Days of Christmas, The
Dating to the 16th century religious wars in England, it was a mnemonic device to teach the catechism secretly to youngsters.
www.cresourcei.org/cy12days.html
Snopes.com: The Twelve Days of Christmas
Considers the legend that the song was created as a coded reference to important articles of the Christian faith.
www.snopes.com/holidays/christmas/12days.asp