What is the symbolism of the ancestor rock in the novel, Touching Spirit Bear?

The Ancestor Rock is a huge rock that Cole carries to the top of a hill on the island every morning. On the way up the hill, the rock represents Cole's ancestors. He is to remember that everything they learned has been passed down. At the top of the hill, he shoves the rock, allowing it to roll back to the bottom. During that, the rock represents Cole's anger and he symbolically lets all his anger go.