How would you summarize the epic poem The Iliad and explain its significance?

I think a lot of people confuse the main theme of this epic. It is not a tale about the Trojan Warbut rather a tale about the wrath of Achilles. The epic begins with his wrath and ends after his wrath is over. Essentially his wrath ends after he kills the mighty Trojan warrior Hektor.
This epic laid the foundations for many epics to come. It invoces a muse(godess of inspiration) to help the poet tell the story, it begins in medias res(in the middle of things), contains supernatural machinery, is told in elevated language, and describes characters who are larger than life.
This epic has influenced authors throughout history and the tales of the Trojan and Greek warriors become important characters to later literature.

Careful not to confuse the main theme of this epic. It is not a tale about the Trojan War but rather a tale about the wrath of Achilles. The epic begins with his wrath and ends after his wrath is over. Essentially his wrath ends after he kills the mighty Trojan warrior Hektor.
This epic laid the foundations for many epics to come. It invokes a muse (goddess of inspiration) to help the poet tell the story, it begins in medias res(in the middle of things), it contains supernatural machinery, it is told in elevated language, and it describes characters who are larger than life.
This epic has influenced authors throughout history and the tales of the Trojan and Greek warriors become important characters in later literature. For example, Achilles appears again in works like the Odyssey, Aeneid, and Dante's Infernowhile Agamemnon becomes an important character in Greek tragedy. The characters and their stories also become important to Western culture. Helen of Troy becomes a worldwide symbol for beauty while "Achilles' heel" is used to describe an individual's weakness. These, of course, are just a few small examples of the poem's far reaching influence.
To sum up how influential this epic has been, the great Roman Empire borrowed a character (Aeneas) from this story and made him the protaginist for their own national epic: Virgil's Aeneid.