I think the main theme of the book is forgiveness....... Cole needs to both forgive and be forgiven.
“Standing beside the totems, he explained to Peter that being invisible was being a part of life’s circle and accepting it. ‘This morning, when we forgave each other, we also forgave ourselves…We allowed ourselves to become a part of the big circle. That’s why we saw the Spirit Bear.’”
Cole to Peter, p. 286
This quote unites many of the book's themes. It explores how Peter, Cole, and others are united in "the big circle" and how forgiveness was essential in order to see truth and healing. The bear at this point becomes very much symbolic in that it appears as a sign that Cole and Peter have found the right path to their personal growth and are ready for the next step of their lives.