Learning more about the Dementors and how to fight them is the continuation of Harry's new stage of magical agency, beginning with his flight from the Dursleys, moving through his willingness to confide in Professor Lupin, and now landing him in these lessons, where he works hard each week to learn how to confront his greatest personal demon. The presence of his parents' voices in his bouts of Dementor "depression" is significant, and to be expected. Harry is constantly aware of his loss of them, and although he never knew his parents, he believes in their love for him, and he battles Voldemort and his servants, in part to protect himself, and in part to avenge their deaths.