Identify two central ideas of the pen "Ulysses" How has the poet developed the ideas?

The first clear idea is the thirst for knowledge, Ulysses reminisces on the "manners, climates, councils, governments," that he encountered during his travels and he uses the metaphor of a "sinking start" for knowledge. Why? Because he knows that he will not be able to following forever and will inevitably "sink" into his death. He thus, longs for one final travel where he will die doing what he loves, to go "beyond the utmost bound of human thought."

The second idea is the yearning for immortality. Indeed, here Ulysses longs not for the home he wanted to come back to after his travels but for his youth. In that sense it can be considered a middle age crisis kind of poem. Since as a human mortal he is unable to escape death and achieve immortality, he will do so by leaving one last time, never to return, in order to perform "Some work of noble note, may yet be done". He wishes to die doing what he did all his life and which he loves, "To strive, to seek, to find, and not to yield" to old age and death.