[The Saucepan Man]

Seems to me InklingElf is spot on with the main theme. The development of the "common man" to hero, through a series of trials. Of course, JRRT intended no allegory, but this is a common theme running through most mythical tales. It was just that JRRT told it well as a children's story. And therein lies much of his skill: to use take the archetypal hero myth and make it into a jolly enjoyable story.