The Divine Comedy by Dante Alighieri is divided into three sections - Inferno, Purgatorio, and Paradiso. Inferno describes Dante's journey through the nine circles of Hell guided by Virgil. Purgatorio details his ascent up the Mountain of Purgatory in seven terraces. In Paradiso, Dante is guided by Beatrice through the nine spheres of Heaven and one Empyrean, seeing blessed souls and angels. The poem discusses the theological concepts of sin, redemption, and the nature of the afterlife through Dante's journey to understand God and achieve spiritual fulfillment.