One of the main points in Virgil’s final Crowning speech is that the Pilgrim has matured in his understanding of the world and of human nature through his climb of the Mount, and that he’s now capable of managing his freedoms to choose his actions in a Good way.
Developing one’s Reason is what should “rule” the nature of our impulses as the threshold of consent, is the claim of Virgil. And as we reach the summit of Mount Purgatory, the Pilgrim has through a long Journey through two books learned an abundance of things about the damaging consequences of some of these impulses, and also how to counter them with Virtues.
Symbolically this is also something we as Readers might experience too, that learning more deeply about the vices and virtues actually changes our perception of the world and how we relate to our instincts and emotions. Which again is Dante the Writer’s argument through Virgil; that this is the first major step towards full happiness and moving towards the state of Felicitá, in Life.