The two central ideas of the poem are to not allow one's life to stay stationary and to find purpose despite being old. Ulysses realized that he did not want to stay in his kingdom living a boring and stationary life. He brought his men to go on adventures and told them that they can still be noble despite being old.
Answer:
The priests said they had a sign from the gods. The Aztecs should settle where they saw an eagle holding a snake while standing on a cactus. They saw this sign on a marshy island in the lake and began to build a new town on the spot.