What are the motifs in The Colour of Magic by Terry Pratchett?

Loyalty is a recurring idea. The Luggage possesses undying loyalty to its owner. Made of sapient pearwood, the Luggage is impervious to magic. This is illustrated in the final scene when the Luggage makes its way toward Twoflower on the Potent Voyager. Magicians are attacking it with every spell in their arsenal, but the Luggage will not be deterred from its mission: to be with its owner.