From the gate of Purgatory, Virgil guides the pilgrim Dante through its seven terraces. These correspond to the seven deadly sins or "seven roots of sinfulness." The classification of sin here is more psychological than that of the Inferno, being based on motives, rather than actions. It is also drawn primarily from Christian theology, rather than from classical sources. The core of the classification is based on love: the first three terraces of Purgatory relate to perverted love directed towards actual harm of others, the fourth terrace relates to deficient love (i.e. sloth or acedia), and the last three terraces relate to excessive or disordered love of good things.
Each terrace purges a particular sin in an appropriate manner. Those in Purgatory can leave their circle voluntarily, but will only do so when they have corrected the flaw within themselves that led to committing that sin.
The structure of the poetic description of these terraces is more systematic than that of the Inferno, and associated with each terrace are an appropriate prayer, a beatitude, and historical and mythological examples of the relevant deadly sin and of its opposite virtue.
First terrace (the proud)
The first three terraces of Purgatory relate to sins caused by a perverted love directed towards actual harm of others.
The first of the sins is pride. On the terrace where proud souls purge their sin, Dante and Virgil see beautiful sculptures expressing humility, the opposite virtue. The first example is of the Annunciation to the Virgin Mary, where she responds to the angel Gabriel with the words Ecce ancilla Dei ("Behold the handmaid of the Lord," Luke 1:38). An example of humility from classical history is the Emperor Trajan, who, according to a medieval legend, once stopped his journey to render justice to a poor widow (Canto X).
Also associated with humility is an expanded version of the Lord's Prayer:
Our Father, You who dwell within the heavens but are not circumscribed by them out of Your greater love for Your first works above, Praised be Your name and Your omnipotence, by every creature, just as it is seemly to offer thanks to Your sweet effluence. Your kingdom's peace come unto us, for if it does not come, then though we summon all our force, we cannot reach it of our selves. Just as Your angels, as they sing Hosanna, offer their wills to You as sacrifice, so may men offer up their wills to You. Give unto us this day the daily manna without which he who labors most to move ahead through this harsh wilderness falls back. Even as we forgive all who have done us injury, may You, benevolent, forgive, and do not judge us by our worth. Try not our strength, so easily subdued, against the ancient foe, but set it free from him who goads it to perversity."
After being introduced to humility, Dante and Virgil meet the souls of the proud, who are bent over by the weight of huge stones on their backs. As they walk around the terrace, they are able to profit from the sculpted examples of humility. The first of these souls is Omberto Aldobrandeschi, whose pride lies in his descent ("I was Italian, son of a great Tuscan: / my father was Guiglielmo Aldobrandesco"), although he is learning to be more humble ("I / do not know if you have heard his name"). Oderisi of Gubbio is an example of pride in achievements – he was a noted artist of illuminated manuscripts. Provenzano Salvani, leader of the Tuscan Ghibellines, is an example of pride in dominating others (Canto XI).
In Canto XIII, Dante points out, with "frank self-awareness," that pride is also a serious flaw of his own:
"I fear much more the punishment below; my soul is anxious, in suspense; already I feel the heavy weights of the first terrace"
After his conversations with the proud, Dante notes further sculptures on the pavement below, this time illustrating pride itself. The sculptures show Satan (Lucifer), the building of the Tower of Babel, King Saul, Arachne, King Rehoboam, and others.
As the poets ascend to the next terrace, an angel brushes Dante's forehead with his wings, erasing the letter "P" (peccatum) corresponding to the sin of pride, and Dante hears the beatitude Beati pauperes spiritu ("Blessed are the poor in spirit," Matthew 5:3) (Canto XII).
Second terrace (the envious)
Envy is the sin that "looks with grudging hatred upon other men's gifts and good fortune, taking every opportunity to run them down or deprive them of their happiness". (This in contrast to covetousness, the excessive desire to have things like money.) As one of the envious souls on this terrace says:
"My blood was so afire with envy that, when I had seen a man becoming happy, the lividness in me was plain to see."
On entering the terrace of the envious, Dante and Virgil first hear voices on the air telling stories of generosity, the opposite virtue. There is, as in all the other terraces, an episode from the life of the Virgin Mary; this time, the scene from the Life of the Virgin is the Wedding at Cana, in which she expresses her joy for the newly married couple and encourages Christ to perform his first miracle. There is also Jesus' saying "Love your enemies." A classical story shows the friendship between Orestes and Pylades.
The souls of the envious wear penitential grey cloaks, and their eyes are sewn shut, resembling the way a falconer sews shut the eyes of a falcon in order to train it. This results in audible, rather than visual, examples here (Canto XIII).
The souls of the envious include Guido del Duca, who speaks bitterly about the ethics of people in towns along the River Arno:
"That river starts its miserable course among foul hogs, more fit for acorns than for food devised to serve the needs of man. Then, as that stream descends, it comes on curs that, though their force is feeble, snap and snarl; scornful of them, it swerves its snout away. And, downward, it flows on; and when that ditch, ill-fated and accursed, grows wider, it finds, more and more, the dogs becoming wolves. Descending then through many dark ravines, it comes on foxes so full of deceit there is no trap that they cannot defeat."
The voices on the air also include examples of envy. The classical example is Aglauros, who (according to Ovid) was turned to stone because she was jealous of Hermes's love for her sister Herse. The Biblical example is Cain, mentioned here not for his act of fratricide, but for the jealousy that led to it (Canto XIV).
As he is leaving the terrace, the dazzling light of the terrace's angel causes Dante to reveal his scientific knowledge, observing that the angle of incidence is equal to the angle of reflection "as theory and experiment will show" (Canto XV).
Third terrace (the wrathful)
On the terrace of the wrathful, examples of meekness, the opposite virtue, are given to Dante as visions in his mind. The scene from the Life of the Virgin in this terrace of purgation is the Finding in the Temple. Whereas most parents would be angry at their child for worrying them, Mary is loving and understanding of Christ's motives behind his three day disappearance. In a classical example, the wife of Peisistratos wanted a young man executed for embracing their daughter, to which Peisistratos responded: "What shall we do to one who'd injure us / if one who loves us earns our condemnation?" Saint Stephen provides a Biblical example, drawn from Acts 7:54–60 (Canto XV):
Next I saw people whom the fire of wrath had kindled, as they stoned a youth and kept on shouting loudly to each other: Kill! Kill! Kill! I saw him now, weighed down by death, sink to the ground, although his eyes were bent always on Heaven: they were Heaven's gates, Praying to his high Lord, despite the torture, to pardon those who were his persecutors; his look was such that it unlocked compassion."
The souls of the wrathful walk around in acrid smoke, which symbolises the blinding effect of anger:
Darkness of Hell and of a night deprived of every planet, under meager skies, as overcast by clouds as sky can be, had never served to veil my eyes so thickly nor covered them with such rough-textured stuff as smoke that wrapped us there in Purgatory; my eyes could not endure remaining open;
Marco Lombardo discourses with Dante on free will – a relevant topic, since there is no point being angry with someone who has no choice over his actions (Canto XVI). Dante also sees visions with examples of wrath, such as Haman and Lavinia.
The prayer for this terrace is the Agnus Dei: "Agnus Dei, qui tollis peccata mundi, miserere nobis... dona nobis pacem" ("Lamb of God, you who take away the sins of the world, have mercy upon us... grant us peace") (Canto XVII).
At this point Virgil is able to explain to Dante the organization of Purgatory and its relationship to perverted, deficient, or misdirected love. The three terraces they have seen so far have purged the proud ("he who, through abasement of another, / hopes for supremacy"), the envious ("one who, when he is outdone, / fears his own loss of fame, power, honor, favor; / his sadness loves misfortune for his neighbor."), and the wrathful ("he who, over injury / received, resentful, for revenge grows greedy / and, angrily, seeks out another's harm."). Deficient and misdirected loves are about to follow (Cantos XVII and XVIII).
Fourth terrace (the slothful)
On the fourth terrace we find souls whose sin was that of deficient love – that is, sloth or acedia. Since they had failed in life to act in pursuit of love, here they are engaged in ceaseless activity. The examples of sloth and of zeal, its opposite virtue, are called out by these souls as they run around the terrace. A scene from the life of the Virgin outlined in this terrace is the Visitation, with Mary going "in haste" to visit her cousin Elizabeth. These examples also include episodes from the lives Julius Caesar and Aeneas. This activity also replaces a verbal prayer for this terrace. Since the formerly slothful are now too busy to converse at length, this section of the poem is a short one.
Allegorically, spiritual laziness and lack of caring lead to sadness, and so the beatitude for this terrace is Beati qui lugent ("Blessed are those who mourn, for they will be comforted," Matthew 5:4) (Canto XVIII and XIX).
Night falls (for the second time) while the poets are on this terrace, and Dante dreams of a Siren (Canto XIX).
Fifth terrace (the covetous)
On the last three terraces are those who sinned by loving good things, but loving them in an excessive or disordered way.
On the fifth terrace, excessive concern for earthly goods – whether in the form of greed, ambition or extravagance – is punished and purified. The avaricious and prodigal lie face-down on the ground, unable to move. Their prayer is Adhaesit pavimento anima mea, taken from Psalm 119:25 ("My soul cleaveth unto the dust: quicken thou me according to thy word,"), which is a prayer expressing the desire to follow God's law (Canto XIX). Dante meets the shade of Pope Adrian V, an exemplar of desire for ecclesiastical power and prestige, who directs the poets on their way.
Further down the terrace, Hugh the Great personifies greed for worldly wealth and possessions. He bemoans the way that, in contrast, avarice has motivated the actions of his successors, and "prophesies" events which occurred after the date in which the poem is set, but before the poem was written:
"The other, who once left his ship as prisoner I see him sell his daughter, bargaining as pirates haggle over female slaves. O Avarice, my house is now your captive: it traffics in the flesh of its own children what more is left for you to do to us? That past and future evil may seem less, I see the fleur-de-lis enter Anagni and, in His vicar, Christ made prisoner. I see Him mocked a second time; I see the vinegar and gall renewed and He is slain between two thieves who're still alive. And I see the new Pilate, one so cruel that, still not sated, he, without decree, carries his greedy sails into the Temple."
These events include Charles II of Naples selling his daughter into marriage to an elderly and disreputable man, and Philip IV of France ("the fleur-de-lis") arresting Pope Boniface VIII in 1303 (a pope destined for Hell, according to the Inferno, but still, in Dante's view, the Vicar of Christ). Dante also refers to the suppression of the Knights Templar at Philip's instigation in 1307, which freed Philip from debts he owed to the order (Canto XX).
In a scene that Dante links to the episode where Jesus meets two disciples on the road to Emmaus, Dante and Virgil are overtaken by the Roman poet Statius, whom Dante presents (on no obvious basis) as a convert to Christianity. He has just finished his time of purgation in this circle, and, as a Christian, his guidance will supplement Virgil's (Canto XXI).
The scene from the life of the Virgin, used here to counter the sin of avarice, is the humble birth of Christ.
Sixth terrace (the gluttonous)
On the sixth terrace are purged the gluttonous, and more generally, those who over-emphasised food, drink, and bodily comforts. In a scene reminiscent of the punishment of Tantalus, they are starved in the presence of trees whose fruit is forever out of reach. The examples here are given by voices in the trees. The Virgin Mary, who shared her Son's gifts with others at the Wedding at Cana, and John the Baptist, who lived on locusts and honey (Matthew 3:4), is an example of the virtue of temperance. A classical example of the opposite vice of gluttony is the drunkenness of the Centaurs that led to the Battle of Centaurs and Lapiths.
The prayer for this terrace is Labia mea Domine (Psalm 51:15: "O Lord, open my lips, and my mouth will declare your praise") These are the opening words from the daily Liturgy of the Hours, which is also the source of prayers for the fifth and seventh terraces (Cantos XXII through XXIV).
Here Dante also meets his friend Forese Donati and his poetic predecessor Bonagiunta Orbicciani. Bonagiunta has kind words for Dante's earlier poem, La Vita Nuova, describing it as the sweet new style. He quotes the line "Ladies that have intelligence of love," written in praise of Beatrice, who he will meet later in the Purgatorio:
"Ladies that have intelligence of Love, I of my lady wish with you to speak; Not that I can believe to end her praise, But to discourse that I may ease my mind. I say that when I think upon her worth, So sweet doth Love make himself feel to me, That if I then should lose not hardihood, Speaking, I should enamour all mankind."
Climbing to the seventh terrace, Dante wonders how it is possible for bodiless souls to have the gaunt appearance of the souls being starved here. In explaining, Statius discourses on the nature of the soul and its relationship to the body (Canto XXV).
Seventh terrace (the lustful)
The terrace of the lustful has an immense wall of flame through which everyone must pass. Souls repenting of misdirected sexual desire (both heterosexual and homosexual) run through the flames calling out examples of lust (Sodom and Gomorrah and Pasiphaë) and of chastity and marital fidelity (the Virgin Mary's chastity). As a prayer, they sing the hymn Summae Deus Clementiae (God of Supreme Clemency) from the Liturgy of the Hours (Cantos XXV and XXVI).
As they circle the terrace, the two groups of penitents greet each other in a way Dante compares to ants:
"There, on all sides, I can see every shade move quickly to embrace another shade, content they did not pause with their brief greeting, as ants, in their dark company, will touch their muzzles, each to each, perhaps to seek news of their fortunes and their journeyings."
Among the flames, which he dare not enter, are the poets of love Guido Guinizelli and Arnaut Daniel, with whom Dante speaks. By reminding Dante that Beatrice can be found in the Earthly Paradise on the other side, Virgil finally persuades Dante to pass through the intense fire (Cantos XXVI and XXVII).
On the stairs to the Earthly Paradise, night falls for the third time, and Dante dreams of Leah and Rachel. They are symbols of the active (non-monastic) and contemplative (monastic) Christian lives, both of which are important (Canto XXVII):
".. in my dream, I seemed to see a woman both young and fair; along a plain she gathered flowers, and even as she sang, she said: Whoever asks my name, know that I'm Leah, and I apply my lovely hands to fashion a garland of the flowers I have gathered. To find delight within this mirror I adorn myself; whereas my sister Rachel never deserts her mirror; there she sits all day; she longs to see her fair eyes gazing, as I, to see my hands adorning, long: she is content with seeing, I with labor."