The Aeneid defines its hero by a quality Roman religion prized and modern readers often find cold. Pietas is not piety in the devotional sense; it is the correct discharge of obligation to gods, to father, to son and to the community, and Aeneas is called pious most often when he is doing something that costs him. The gods in the poem act constantly and are not in charge. Juno delays and cannot prevent, Jupiter states what is fated rather than deciding it, and the whole machinery serves an outcome none of them authored.
Book six is the part with the largest religious content. Aeneas obtains the golden bough, goes down with the Sibyl of Cumae, passes the unburied dead who must wait a hundred years on the wrong bank, and reaches the fields of the blessed, where his father explains the arrangement: a fiery spirit runs through all things, bodies clog and stain it, and after death the stain must be purged by wind, water or fire, after which most souls are called to the river of forgetting and sent back into bodies again. That is a doctrine of transmigration and purification embedded in the Roman national epic, and it sits oddly with everything else in the poem. Aeneas then leaves through the gate of ivory, which is the gate of false dreams, and Virgil offers no explanation for that at all.