What is the moral lesson in canto 3?

In Canto III of Dante's Inferno, the moral lesson is that those who succumb to gluttony become enslaved to their lust and gluttony and forfeit God's love which deprives them of the capacity to repent or escape. This leads them to a life of constant dissatisfaction and ultimately damnation. It serves as a warning against overindulgence, excessive attachment to worldly pleasures, and neglecting one's spiritual life. Instead, individuals must strive for moderation, self-discipline, and seeking higher purpose and fulfilment.