The Roman ideal of pietas ("piety, dutiful respect"), which can be loosely translated from the Latin as a selfless sense of duty toward one's filial, religious, and societal obligations, was a crux of ancient Roman morality. Throughout the Aeneid, Aeneas serves as the embodiment of pietas, with the phrase "pious Aeneas" occurring 20 times throughout the poem, thereby fulfilling his capacity as the father of the Roman people. For instance, in Book 2 Aeneas describes how he carried his father Anchises from the burning city of Troy: "No help/ Or hope of help existed./ So I resigned myself, picked up my father,/ And turned my face toward the mountain range." Furthermore, Aeneas ventures into the underworld, thereby fulfilling Anchises' wishes. His father's gratitude is presented in the text by the following lines: "Have you at last come, has that loyalty/ Your father counted on conquered the journey? 
However, Aeneas's pietas extends beyond his devotion to his father; we also see several examples of his religious fervour. Aeneas is consistently subservient to the gods, even if it is contradictory to his own desires, as he responds to one such divine command, "I sail to Italy not of my own free will."
In addition to his religious and familial pietas, Aeneas also displays fervent patriotism and devotion to his people, particularly in a military capacity. For instance, as he and his followers leave Troy, Aeneas swears that he will "take up/ The combat once again. We shall not all/ Die this day unavenged."
Aeneas is a symbol of pietas in all of its forms, serving as a moral paragon to which a Roman should aspire.
One of the most recurring themes in the Aeneid is that of divine intervention. Throughout the poem, the gods are constantly influencing the main characters and trying to change and impact the outcome, regardless of the fate that they all know will occur. For example, Juno comes down and acts as a phantom Aeneas to drive Turnus away from the real Aeneas and all of his rage from the death of Pallas. Even though Juno knows in the end that Aeneas will triumph over Turnus, she does all she can to delay and avoid this outcome.
Divine intervention occurs multiple times in Book 4 especially. Aeneas falls in love with Dido, delaying his ultimate fate of traveling to Italy. However, it is actually the gods who inspired the love, as Juno plots:
Dido and the Trojan captain [will come] To one same cavern. I shall be on hand, And if I can be certain you are willing, There I shall marry them and call her his. A wedding, this will be.
Juno is speaking to Venus, making an agreement and influencing the lives and emotions of both Dido and Aeneas. Later in the same book, Jupiter steps in and restores what is the true fate and path for Aeneas, sending Mercury down to Aeneas's dreams, telling him that he must travel to Italy and leave his new-found lover. As Aeneas later pleads with Dido:
The gods' interpreter, sent by Jove himself-- I swear it by your head and mine-- has brought Commands down through the racing winds!..... I sail for Italy not of my own free will.
Several of the gods try to intervene against the powers of fate, even though they know what the eventual outcome will be. The interventions are really just distractions to continue the conflict and postpone the inevitable. If the gods represent humans, just as the human characters engage in conflicts and power struggles, so too do the gods.
Fate, described as a preordained destiny that men and gods have to follow, is a major theme in the Aeneid. One example is when Aeneas is reminded of his fate through Jupiter and Mercury while he is falling in love with Dido. Mercury urges, "Think of your expectations of your heir,/ Iulus, to whom the whole Italian realm, the land/ Of Rome, are due." Mercury is referring to Aeneas's preordained fate to found Rome, as well as Rome's preordained fate to rule the world:
He was to be rule of Italy, Potential empire, armorer of war; To father men from Teucer's noble blood And bring the whole world under law's dominion.
It is important to recognize that there is a marked difference between fate and divine intervention, as even though the gods might remind mortals of their eventual fate, the gods themselves are not in control of it. For example, the opening lines of the poem specify that Aeneas "came to Italy by destiny," but is also harassed by the separate force of "baleful Juno in her sleepless rage."  Even though Juno might intervene, Aeneas's fate is set in stone and cannot be changed.
Later in Book 6 when Aeneas visits the underworld, his father Anchises introduces him to the larger fate of the Roman people, as contrasted against his own personal fate to found Rome:
So raptly, everywhere, father and son Wandered the airy plain and viewed it all. After Anchises had conducted him To every region and had fired his love Of glory in the years to come, he spoke Of wars that he might fight, of Laurentines, And of Latinus' city, then of how He might avoid or bear each toil to come.
Violence and conflict
From the very beginning of the Aeneid, violence and conflict are used as a means of survival and conquest. Aeneas's voyage is caused by the Trojan War and the destruction of Troy. Aeneas describes to Dido in Book 2 the massive amount of destruction that occurs after the Greeks sneak into Troy. He recalls that he asks his men to "defend/ A city lost in flames. Come, let us die,/ We'll make a rush into the thick of it." This is one of the first examples of how violence begets violence: even though the Trojans know they have lost the battle, they continue to fight for their country.
This violence continues as Aeneas makes his journey. Dido kills herself in an excessively violent way over a pyre in order to end and escape her worldly problem: being heartbroken over the departure of her "husband" Aeneas. Queen Dido's suicide is a double edged sword. While releasing herself from the burden of her pain through violence, her last words implore her people to view Aeneas's people with hate for all eternity:
This is my last cry, as my last blood flows. Then, O my Tyrians, besiege with hate His progeny and all his race to come: Make this your offering to my dust. No love, No pact must be between our peoples.
Furthermore, her people, hearing of their queen's death, have only one avenue on which to direct the blame: the already-departed Trojans. Thus, Dido's request of her people and her people's only recourse for closure align in their mutual hate for Aeneas and his Trojans. In effect, Dido's violent suicide leads to the violent nature of the later relationship between Carthage and Rome.
Finally, when Aeneas arrives in Latium, conflict inevitably arises. Juno sends Alecto, one of the Furies, to cause Turnus to go against Aeneas. In the ensuing battles, Turnus kills Pallas, who is supposed to be under Aeneas's protection. This act of violence causes Aeneas to be consumed with fury. Although Turnus asks for mercy in their final encounter, when Aeneas sees that Turnus has taken Pallas' sword belt, Aeneas proclaims:
You in your plunder, torn from one of mine, Shall I be robbed of you? This wound will come From Pallas: Pallas makes this offering And from your criminal blood exacts his due.
This final act of violence shows how Turnus' violence—the act of killing Pallas—inevitably leads to more violence and his own death.
It is possible that the recurring theme of violence in the Aeneid is a subtle commentary on the bloody violence contemporary readers would have just experienced during the Late Republican civil wars. The Aeneid potentially explores whether the violence of the civil wars was necessary to establish a lasting peace under Augustus, or whether it would just lead to more violence in the future.
Written during the reign of Augustus, the Aeneid presents the hero Aeneas as a strong and powerful leader. The favorable representation of Aeneas parallels Augustus in that it portrays his reign in a progressive and admirable light, and allows Augustus to be positively associated with the portrayal of Aeneas. Although Virgil's patron Maecenas was obviously not Augustus himself, he was still a high figure within Augustus' administration and could have personally benefitted from representing Aeneas in a positive light.
In the Aeneid, Aeneas is portrayed as the singular hope for the rebirth of the Trojan people. Charged with the preservation of his people by divine authority, Aeneas is symbolic of Augustus' own accomplishments in establishing order after the long period of chaos of the Roman civil wars. Augustus as the light of savior and the last hope of the Roman people is a parallel to Aeneas as the savior of the Trojans. This parallel functions as propaganda in support of Augustus, as it depicts the Trojan people, future Romans themselves, as uniting behind a single leader who will lead them out of ruin:
New refugees in a great crowd: men and women Gathered for exile, young-pitiful people Coming from every quarter, minds made up, With their belongings, for whatever lands I'd lead them to by sea.
Later in Book 6, Aeneas travels to the underworld where he sees his father Anchises, who tells him of his own destiny as well as that of the Roman people. Anchises describes how Aeneas's descendant Romulus will found the great city of Rome, which will eventually be ruled by Caesar Augustus:
Turn your two eyes This way and see this people, your own Romans. Here is Caesar, and all the line of Iulus, All who shall one day pass under the dome Of the great sky: this is the man, this one, Of whom so often you have heard the promise, Caesar Augustus, son of the deified, Who shall bring once again an Age of Gold To Latium, to the land where Saturn reigned In early times.
Virgil writes about the fated future of the city that Aeneas will found, which will in turn lead directly to the golden reign of Augustus. Virgil is using a form of literary propaganda to demonstrate the Augustan regime's destiny to bring glory and peace to Rome. Rather than use Aeneas indirectly as a positive parallel to Augustus as in other parts of the poem, Virgil outright praises the emperor in Book 6, referring to Augustus as a harbinger for the glory of Rome and new levels of prosperity.