Love and duty are at odds in Book IV, and this is shown in the love Dido feels for Aeneas and the responsibility Aeneas feels for resuming his duties.
Dido's love is a violent force because her emotions have destroyed her self-control. It is like an "inward fire eating her away", and she abandons her duties to her people because of it. She no longer cares about building Carthage, and her people hate her selfish actions. At the end of Book IV, she kills herself, and Virgil, comparing her suicide to a city that has been overrun by its enemies, describes her death "As though ... flames billowed on the roofs of men and gods". Her love for Aeneas has brought only death, hatred, and destruction. She allows her emotions as a woman to replace her duties as a leader.
Aeneas views his love of Dido as a temporary distraction from his real duties and responsibilities. Mercury reminds him of his destiny, and Aeneas, even though conflicted, leaves Dido. He "struggle[s] with desire to calm and comfort [Dido] in all her pain", but love can never supersede his duties. Aeneas returns to his civic responsibilities, leading the people of Carthage to his new city.
Book IV drives home the point that Dido's duty as a woman triumphs over love.
Because the reader has known from the start that Dido’s love for Aeneas cannot survive, it is impossible not to feel pity for Dido. Her fall is terrible because she is initially so great, having survived the treacherous murder of her husband and successfully led her people to a new kingdom - an achievement made greater because she is a woman in an ancient patriarchal world.
It is not Dido’s flaws that cause her destruction: it is a conspiracy against her by the unfeeling gods. Her initial love for Aeneas was planted in her through the deceit of Venus. The unhealthy nature of the goddess-given love is brought out in the narrative’s reference to it as a “shaft of death” that is driving her to distraction (97). It is no wonder that Dido was the first successful female character in Latin literature, eventually appearing as a heroine in the works of Chaucer, Marlowe, and the operas of Berlioz and Purcell.