What are the motifs in A Dog's Purpose by W. Bruce Cameron?

The idea of loyalty runs throughout the book. The dog feels loyalty to any person who is kind to it. In his first lifetime, he feels loyalty to Senora. In his second lifetime, he feels tremendous loyalty to Ethan. He tries to please him every way he can and attack Todd with a primal rage when Todd endangers Ethan by setting fire to Ethan's house. In his third lifetime as a female German Shepherd, she feels loyalty to her two handlers and obeys them unquestioningly.