Have you ever heard the song, "The Twelve Days of Christmas," being a sort of underground catechism? Actually, there is no proof that that's true. On the other hand, there's no proof that it isn't.
I like to think of it as a memory help to learn the Christmas story. In days when children learned to read by using the Bible as a Reader, why wouldn't the Christmas story be a way of learning catechism?
Today, Christmas is the first day. And A Partridge in a Pear-Tree is given as a present. There is a myth of Perdix and Athena. Perdix is Latin for the lost one (Adam). The King of Athens fell into the sea. (Fell from grace) but was miraculously transformed into a partridge (the new Adam) by the Goddess Athena, whose symbol was the pear-tre,e and who was called the Mind of Zeus (Divine Logos) and carried to heaven by her. Thus, the partridge in a pear-tree emphasized the union of Christ's human and Divine natures.