It has often been remarked that the Iliad is a poem primarily about kleos, while the Odyssey is concerned with nostos. This is partly true. Homecoming is clearly the subject of the Odyssey, though Odysseus is as concerned with kleos as any Greek hero and sometimes endangers himself...
It has often been remarked that the Iliad is a poem primarily about kleos, while the Odyssey is concerned with nostos. This is partly true. Homecoming is clearly the subject of the Odyssey, though Odysseus is as concerned with kleos as any Greek hero and sometimes endangers himself and his men for the sake of it, as when he calls out his name to Polyphemus when fleeing from the land of the Cyclopes.
In the Iliad, much of the poignancy is derived from the fact that so many of the Greek heroes will never return home again. The Trojans will very soon have no home. Even the homecoming of the victorious Agamemnon will be as far as possible from the traditional nostos, since he will be murdered almost immediately. The Greek heroes have given up (and the Trojan heroes have been forced to give up) the simple delights of home for the chance to win glory.
The theme of kleos is the primary reason why the quarrel between Agamemnon and Achilles that dominates the beginning of the Iliad is so bitter, at least from the perspective of Achilles. Achilles has given up the chance to grow old peacefully at home, not to retrieve Menelaus's wife or to conquer territory for Agamemnon, but to win glory for himself. Agamemnon treats him like a vassal, and it is this which leads Achilles to decide there is no point in fighting. Even when Agamemnon sends an embassy with magnificent gifts in Book IX, there is no apology or respect from the high king, which is why Achilles refuses angrily and dismisses the emissaries. There is no kleos in being Agamemnon's servant, however well-paid.
Nostos is “homecoming,” and Kleos is “honor.” Nostos is really the main theme of the Odyssey, not the Iliad, but it is certainly present as an underlying theme in the Iliad, a story in which the war has dragged on for ten years and everybody very much wants to return home. Interestingly, when the Trojans make their attack in which Patroclus dies, they set fire to the Achaean ships to prevent them from leaving—really, to destroy their resources and turn it into a siege on the Achaeans by trapping them at the shoreline, but what they effectively do is turn them into cornered animals and escalate the situation severely by denying them a chance to go home.
Kleos is the main theme of the Iliad because honor is the whole reason they’re all there in the first place. They swore to support Menelaus in keeping Helen, so they’re all dragged into this theater of war, and it is concern for honor that prevents them from giving up and going home. Achilles is only there for his own personal honor (because he knows he’s doomed to die young, and the only way to make his life worthwhile is to perform honorable deeds). Consequently, when Achilles is ready to personally surrender and return home (nostos), this precipitates the crisis that forms the core of the narrative. Achilles cannot leave, because it would be dishonorable. He knows the only worthwhile life is one where he dies young in a blaze of glory (the alternative is dying old and unremarked). But why should he stay when, arguably, he hasn’t got any obligations to be there? He wants to leave. Only his own fate, and the web of arguments from all sides that it’s dishonorable to leave when the Achaeans really need him, keeps him in place. Ultimately, however, Achilles's decision to leave throws into sharp relief the sheer futility of the decade-long war, prompting the question: why can't everyone else also simply make the decision to leave?
In the society depicted by Homer, nostos and kleos are two of the major tenets of Ancient Greece. Nostos refers to a warrior's journey home by sea, a sign of victory and prosperity. Kleos means "glory" or "renown"—specifically the kind of glory and renown that become the stuff of legend. The Greek warriors in the Iliad long for both a journey home by sea and glory; victory in war and becoming the subject of legends was considered the greatest thing to which a warrior could aspire.
These two themes are especially significant with Achilles, who knows that if he is to achieve kleos, he cannot have nostos. When Odysseus comes to recruit Achilles, Achilles is given a choice: either fight in the Trojan War and die a legend, or stay home and live a long and peaceful life but ultimately fade from memory. Achilles is resolved that even though his life will be short, he will achieve immortality through his glory.
In Homer's Iliad, the epic poet's heroes are often motivated by kleos, a Greek word which can carry meanings such "good reputation", "fame", and "glory." In the opening of Iliad 5, for example, goddess Athena inspires Diomedes so that "he’d stand out and win heroic glory [kleos]" (A.S. Kline translation). In Iliad 9, after Achilles withdraws from the fighting, we find him in his tent singing (ironically) of the glorious deeds of other warriors. Thus, for Homeric heroes such as Diomedes and Achilles, the achievement of glorious deeds is a significant motivation. Failure to achieve such deeds would make them rather ordinary men.
As for the concept of nostos, which means "return" or "return home," this is a theme dealt with more frequently in the Odyssey than the Iliad. The Odyssey focuses almost entirely on Odysseus' nostos. Still, nostos versus kleos is a choice that Achilles must face. At Iliad 9.413, Achilles must decide between going back to Greece and living to old age, or remaining at Troy and dying young, but gaining everlasting glory. Hector's onslaught against the Greek camp and his threatening to set fire to the Greeks' ships will take away Achilles' nostos (Iliad 16.82), so Patroclus begs Achilles to let him lead their troops into battle. When Achilles agrees and Patroclus goes into battle and is killed by Hector, this event seems to seal the fact that Achilles will not return home, but will stay at Troy, kill Hector, and gain everlasting kleos.