By channeling his anger into something productive—standing up for the first time—Colin shows that he's beginning to grasp the power of positive thinking. Mary's whispering helps channel that positive thinking, something that Colin will later insist is a spell. All of the rumors that Ben mentions shows that at least some of what ails Colin is the rumors, which make it so nobody else (aside from Mary and now Dickon) can act as a mirror and tell him he's fine.