Many of the adventures the travelers had in Rasselas, Prince of Abyssinia led to revelations and deeper understanding.
Ye who ... pursue ... hope; who expect ... the promises of youth, ... attend to the history of Rasselas, Prince of Abyssinia
Three of these that stand out as most important might be as follows. First, Rasselas and his companions meet and talk to every sort of person in every sort of situation in life, from the very high to the very low. What they discover, which is part of Johnson's message, is that none were satisfied, each desired more and envied what others had. None were truly happy because of this dissatisfaction, desire, and envy.
Second, Rasselas and his friends met a wise philosopher who taught his followers that a life built upon reason will lead to happiness because reason will quell the sting of emotional passions and the heartbreak of disappointments. Yet, when his daughter died, the philosopher was inconsolable: Reason had abandoned him being unable to quell the pain of truth and suffering. Here they discovered that none could be truly happy based upon reason alone because life deals blows that devastate the emotions and the power of reason.
Third, Pekuah (Nekayah’s maid) is abducted and held for a very long while a ransom for her is arranged. During this time Pekuah is housed in a monastery (which is rather odd in and of itself since a religious order is thus shown aiding and abetting an abduction ...) and comes to see a religious life as the only truly happy life. None of the others are enthusiastic in sharing her opinion and, in the end, it isn't tested as they decide it is time to return to Happy Valley. Petukah's abduction does influence Nekayah (Rasselas' favorite sister) to contemplate the nature of the soul leading to a discourse while at the catacombs. She decides that it is not possible to find a truly happy person and thus she will will abandon the quest for earthly happiness and pursue a quest for happiness of the soul by living so as to find happiness in eternity: "the choice of life is become less important; I hope hereafter to think only on the choice of eternity."
The final outcome is they each reveal their inner desires, decide that their desires are never to be fulfilled (as no one else’s are), and agree to return to Happy Valley with more wisdom and a better understanding of the important things in life--like what is most suitable and what will give satisfaction and where is one's destiny--even if they return without the knowledge of where and how to attain true happiness.
It was now the time of the inundation of the Nile. A few days after their visit to the catacombs the river began to rise. ... They deliberated awhile what was to be done, and resolved, when the inundation should cease, to return to Abyssinia.