what was the authors purpose for writing the book?

I think the author wanted to illustrate the racial injustice towards indigenous peoples which includes the horror of residential schools. After Saul was taken in by his adoptive family, he escaped the violence he was subjected to in school but had instead to endure the way the Natives were treated by the white Canadians. Many hokey players and teams refused to play against the Moose for the simple reason that they were Indians. What is more, the Indian players were often treated with more violence on the ice and the crowd would shout racial slurs at them. At times, the white people would even become violent after games and would physically attack the Indian players. Saul notes that some white players even refuse to have any type of skin contact with the Indian players, refusing even to shake their hands.