If you really want to know the major themes of the Aeneid, here they are.
1. The Roman hero. Aeneas is in a way a Homeric hero without the bluster and with a more profound and civilised approach to life and the gods.
2. Humanity. There is poor old Aeneas, just like the rest of us, stuck on the horns of a very human dilemma: do I leave Dido and carry out my duty, or do I follow my heart and stay here? We know that the epic wouldn't have been written if he had made a different decision - but of course nor would Roma have been founded. He would have hung around in Carthage. Instead he mkes his way to Italy and sets up the Roam approach.
Rome. Aeneas, without knowing the future - except what he is told by his father in the underworld - complies with what he understands to be correct. He is also given nudges about what has to happen during the fall of Troy, where he can see that the collapse of Troy is pa\rt of the Gods' plan, as they help pull down the walls. Accordingly he realises that he has a future elsewhere.
If Virgil was entirely lacking compassion and committed to Rome rather than to the reality of human weakness, he would have been able to exclude the Dido episode. In fact he exploits it as a genuine example of the way we operate.
This may seem a personal response to the Aeneid; but anything else would be less, would miss the point.
There is much more that could be said in detail but that will do for now. Essentially we have the political background, the human truths and the personal issues. They combine into a visionary whole. I cannot escape any aspect of the poem, since I think they are intertwined.
awh