The work's numerology carries deep meaning. Written in terza rima (interlocking three-line stanzas), it reflects the Trinity. Each realm contains 33 cantos (plus Inferno's introduction), totaling 100—a number of completion. Hell has nine circles plus vestibule; Purgatory has seven terraces plus ante-purgatory and earthly paradise; Paradise has nine spheres plus the Empyrean.
The structure reflects medieval theology's precision: sins in Hell are punished by contrapasso (poetic justice), virtues in Purgatory are purified, and in Paradise, souls exist in perfect harmony according to their capacity for divine love. The concentric circles of Hell mirror the ascending mountain of Purgatory and the nested spheres of Paradise.
Dante synthesized classical learning, Christian theology, and medieval cosmology into a unified artistic vision that mapped the soul's journey from sin through purification to beatific union with God.
Source
Divine Comedy - Dante Alighieri