The petrification of the little party of small animals is really the first tragedy that we have witnessed firsthand in the novel. We know that the Witch is evil, cruel, and will gladly murder others, but we have so far only heard about her character indirectly. So, too, has Edmund. He realizes that Aslan's side is the good one when the Witch treats him poorly, but his belief is initially superficial. Edmund expresses that he does not enjoy being cold, tied up and miserable. Lewis, however, tells us that when Edmund sees the feasting animals turned to stone, "for the first time in this story [he] felt sorry for someone besides himself." Edmund is affected very deeply, and he shifts from self- interest to empathy and pity. Edmund can be misled but he is not fundamentally evil. Edmund's actions up until now have been spiteful and self-serving, but his core of essential goodness has not died, as it perhaps never does in a human being.
Lewis suggests that any sinner, like Edmund, can be reformed, given the right circumstances and an open mind. In Edmund's case he was the object of the Witch's wrath himself and then witnessed the petrification of the animals at feast. This does not make him immune to future temptation and conflict. Edmund has taken the first steps toward reformation, but his redemption is not yet complete. The most important step has already been made, however, as he feels compassion for the poor animals. This does not affect him personally or directly in any way, and his ability to feel emotions for others shows that he has begun to change.
Peter's fight with the wolf represents a fundamental change for him as well: from child to adult. Aslan could easily have slain the wolf himself, or allowed the other animals to do it, with far less risk to Susan and Peter. Instead, Aslan relies on Peter, who has never wielded a sword before. This appears unnecessarily dangerous, but Aslan's actions are intentional and appropriate. Peter, as the oldest, will be the High King, so it is essential that he fight his own battles and gain experience. Aslan could set him on the throne gently, without Peter ever facing danger, and he might do well, reigning justly and with kindness. But Peter would then be incomplete. To reign properly, Peter must discover the valor and bravery within him. Aslan knew that Peter could kill the wolf, but Peter needed to actually do this to become confident in his own strength and ability. Peter's defining personality traits are his courage, strength, and ability to lead others without misusing his power. Aslan insists that Peter fight for Susan alone because it is this battle that initiates Peter's transformation to adulthood.