At the beginning of Chapter 1, Mill lays out a brief overview of why people have traditionally looked to an authority figures for protection. In this case, he uses a series of violent similes and metaphors to demonstrate the complicated role that such figures can play:
Their power was regarded as [...] a weapon which they would attempt to use against their subjects, no less than against external enemies. To prevent the weaker members of the community from being preyed upon by innumerable vultures, it was needful that there should be an animal of prey stronger than the rest, commissioned to keep them down. But as the king of the vultures would be no less bent upon preying on the flock than any of the minor harpies, it was indispensable to be in a perpetual attitude of defence against his beak and claws.
Although Mill has already admitted before this that authoritarian power can be necessary, these literary devices make clear that their power can also be deadly. Mill uses his simile to compare a ruler with a weapon, and, through metaphor, to an animal of prey that could protect "weaker" citizens from "innumerable vultures" (any number of stronger citizens or threats they might face).
Though this might seem to be an absolute good, any such animal of prey could turn also against the weaker populace they have been set up to protect. Thus, Mill emphasizes the importance of a careful, guarded, naturally suspicious relationship between a population and its ruler. This is a vital example of Mill's give-and-take understanding of liberty and authority in his essay.
In Chapter 2, Mill impresses upon the reader the importance of having some self-awareness about one's worldview and beliefs. Using allusion, he reminds the reader that every age, and every society, has people who believe what they believe to be true according to their faiths and their lived experiences, and it's just as likely that—if one were to be born halfway across the world—they'd find these different perspectives totally acceptable. Ultimately, the most important thing is to remember how every "age" will believe things that, in the future, will seem "absurd," just like past beliefs seem absurd in the present age:
[...] it never troubles him that mere accident has decided which of these numerous worlds is the object of his reliance, and that the same causes which make him a Church-man in London, would have made him a Buddhist or a Confucian in Pekin. Yet it is as evident in itself, as any amount of argument can make it, that ages are no more infallible than individuals; every age having held many opinions which subsequent ages have deemed not only false but absurd; and it is as certain that many opinions now general will be rejected by future ages, as it is that many, once general, are rejected by the present.
Mill's argument relies on allusions to the local religion of various significant civilizations: the Anglican Church in London and the beliefs of Buddhism and Confucianism in Pekin (now Beijing), China. Depending on the time and place of one's birth, one could hold any number of opinions that seem to be absolutely true but that are seen as ridiculous in another place or at a later time.
Mill's observation fits in with his exploration of morality, new ideas, and progress throughout his essay. He is arguing that humanity must be well aware of its fallibility and must never think any of its ideas unassailable, given that the march of time and progress will always bring new ideas and beliefs that conflict with or even entirely supersede the old.
