Divine Comedy: Novel Summary: Purgatorio section 17- Purgatorio section 21

 Purgatorio section 17: The poets emerge from the smoky cloud near sunset.  Again, Dante receives visions of wrath: Procne (who killed her son), the execution of Haman, and Lavinia (who discovered the body of her mother who had hanged herself).  After the visions pass, an angel beckons Dante to mount the stairs to the Fourth Terrace where the Slothful reside.  The angel brushes another P from Dantes forehead.  As Dante climbs the stairs he hears the Seventh Beatitude, “Beati pacifici” (Blessed are the peacemakers).  Night has fallen when the travelers reach the next level so the two rest.  To pass the time, Virgil outlines the design of Purgatory.  Virgil explains that all action, good and evil, stems from some form of love.  There are two forms of love, instinctual love and chosen love (love that stems from ones mind).  Natural (instinctual) love is perfect in the eyes of God but chosen love emerges from mans free will and is, therefore, prone to error.  Love that aims to hurt others takes form in pride, envy, and wrath-the sins found on the first three terraces.  Love directed toward a worthy end but with insufficient zeal, sloth, is punished on the Fourth Terrace.  The three upper terraces punish sinners who loved earthly objects excessively.  Virgil does not reveal the sins punished on the three upper terraces.
Purgatorio section 18: Virgil continues his discussion of love and free will: “The soul, which is created quick to love, responds to everything that pleases, just as soon as beauty wakens it to act.Then, just as flames ascend because the form of fire was fashioned to fly upward, toward the stuff of its own sphere, where it lasts longest, so does the soul, when seized, move into longing, a motion of the spirit, never resting till the beloved thing has made it joyous.” However, while instinctual love is natural, like the flames of a fire, men exert free will.  Free will can pervert natural love and men are judged by their acts of free will.  Virgil states, “Now that all other longings may conform to this first will [instinctual love], there is in you, inborn, the power that counsels [free will], keeper of the threshold of your assent: this principle on which your merit may be judged, for it garners and winnows good and evil longings.” As Virgil concludes his explanation, the poets hear a group of spirits approach.  In great haste, the spirits recite examples of zeal (the opposite of their own sin, sloth) as they hurry by.  Virgil asks the souls for directions to the next terrace as Dante falls asleep.
Purgatorio section 19: In a dream, Dante encounters a Siren that sings to him sweetly and tries to tempt him as she tempted Ulysses.  Virgil rips the clothes off of the Siren to expose her ugliness and corruption.  Startled, Dante awakens from his dream as an angel approaches to lead the poets to the next level.  The angel pronounces the Third Beatitude, “Qui lugent” ([Blessed are] those who mourn).  As they climb to the next plain, Virgil explains to Dante that the Siren caused the sins of those who reside above on the mountain.  To guard against the Sirens seductions, men must “fasten [their] eyes upon the lure thats spun by the eternal King” (men must keep their eyes on Heaven).  On the Fifth Terrace-reserved for the Avaricious and the Prodigal, Dante finds numerous spirits lying face down on the ground singing “Adhesit pavimento anima mea” (My soul has adhered to the ground).  Dante questions a nearby spirit who explains that he was avaricious (he loved earthly possessions) until he became a pope.  Since he did not turn his eyes toward Heaven until late in life, he must spend his time in Purgatory groveling for penance face down in the dirt.  Dante bows out of respect for this former pope but the spirit admonishes him to stand because in the spirit world everyone is an equal servant of God. 
Purgatorio section 20: Dante and Virgil stay close to the wall as they move along this terrace because so many souls crowd the ground.  Dante calls avarice a “she-wolf” which has claimed the most souls of any sin.  Dante hears a voice citing the poverty of Mary as an example of virtue opposite avarice.  The voice continues by citing two more examples: Fabricius, a Roman counsel who rejected a bribe, and St. Nicholas, who saved his sisters from degradation by earning dowries for them.  Dante finds the spirit whose voice he just heard and learns that it belongs to Hugh Capet, the founder of a grand French dynasty.  In a long and specific list of the crimes committed by French royalty, Capet denounces the sins of his children and kinsmen and prophesies future treachery.  Capet tells Dante that the penitents on this ledge recite examples of poverty and generosity during the day and decry examples of avarice during the night.  Capet gives several examples of Avarice: Pygmalion, Midas, and Heliodorus.  As the poets leave Capet, Dante feels a tremendous earthquake.  The spirits cry “Gloria in excelsis Deo” then continue their recitals with more zeal than before.
Purgatorio section 21: Still on the Fifth Terrace, Dante dwells on the source of the earthquake that he just experienced.  A spirit approaches the travelers from behind and demands to know whey Dante has come to Purgatory.  Virgil explains that their journey was designed in Heaven and that although he is consigned to Limbo, Virgil must act as Dantes guide.  In response to Dantes query about the earthquake, the spirit explains that Purgatory quakes every time a spirit completes its penance and rises to Heaven.  Each time this happens, the remaining spirits praise the Lord.  The spirit, calling himself Statius, claims that the last quake signaled his own deliverance from Purgatory.  Without recognizing Virgil standing before him, Statius remarks that his inspiration in life was the great poet.  Dante reveals the name of his guide and Statius bows down before Virgil in great reverence and awe.