In the second part of the poem, Ulysses explains the difference between himself and his son Telemachus. His son will be a fair and decent ruler to his people, but the political life in this context is boring. Telemachus is obliged to a regular political life, where the aspiration is to lead a rough populace into accepting a better vision of morality and expedience. It is a duty that a leader of uninspired and imprudent citizens may well satisfy with honor, like satisfying one’s regular duty to honor the “household gods.” But to Ulysses this “slow” life is intolerable even if somebody has to do it. Thus Telemachus “works his work, I mine.”

In the third part Ulysses seems to address his hearty mariners. The port, the boat, and the seas. The mariners are his compatriots; they have been through thick and thin together. Unlike living under a king, on the seas they made their choices and took their risks with “free hearts, free foreheads.” Those were the good old days, even fighting with gods, but there is no good reason to waste away in nostalgia. Although the coming night in the poem reflects the years of their lives, it “is not too late to seek a newer world.” The “many voices” calling them are the voices of experiences past and of experiences yet to come. Their life is fulfilling when they are adventuring on the sea, no matter how much strength they have.
The allusion to Achilles in the Happy Isles draws a contrast to Hades. In Homer’s Iliad, Achilles is the featured warrior whose anger and valor generate the primary storyline. He is a hero who lived his life in Troy, once he got back into the battle. But for much of the Iliad, Achilles sulked in his tent and left his sword and his skills “unburnish’d.” Accordingly, Achilles is a good model of heroism for Ulysses.
For Ulysses, the crisis is due to old age: he knows death is unavoidable, but he also knows that death-in-life is intolerable for a person like him. It may be argued that Ulysses seeks to understand life beyond death, but consider that “it may be” that they reach the isles where Achilles resides. Ulysses may indeed want to find direct evidence of spiritual reality after death.
But the real, final point is: as honorable as it may be to live a peaceful life without risk, we miss the most exciting aspects of life if we do not venture out, at least a little bit, into the unknown.