Though they are old, Ulysses asks his mariners, the men with whom he has experienced so many great adventures, to strike out with him again, in search of "a newer World."
Death closes all; but something ere the end,
Some work of noble note, may yet be done,
Not unbecoming men that strove with gods.
Men like Ulysses and his followers were not intended to live out their lives in peace and quiet, but to continue to challenge themselves and seek adventure. Time has made them older, but the spark that made it possible for them to contend with the hardships and the challenges they faced earlier in life is still present, and Ulysses is saying that it would be a shame if it were wasted. Tennyson also associates the Greek hero with an element of intellectual curiosity, a desire to see all the world has to offer before death. Ultimately, Ulysses is claiming that while a life of struggle might be dangerous, to live a sedentary life is a fate worse than death for people like him and his mariners.