Central to the novel is the character of Tarunculus, whose tragedy is that he has the potential to become a good man, but does not because he cannot let go of the big picture.
By 'big picture' I mean his obsession with the Roman Empire, its survival and glory. To that obsession he sacrifices everything and ultimately loses everything. He has an illness common in contemporary society, the notion that a life that is not humanly significant is meaningless.
What do I mean by 'significant'? I mean doing something that has a major impact on society, something which raises one above the obscurity of one's common and unremarkable fellow-men. The desire to do something significant can go with a sincere aim of improving things or with a simple desire for prestige. Either way, if it does not meet with success, it leaves the conviction that life is pointless. This is the motivator behind ambition, the notion that a life that is not significant is futile. Someone with this disease cannot grasp the fact that an obscure life is not necessarily a failed one. Simple maths tells you that. Someone who stands out from the others must have others to stand out from. If everybody stood out then nobody would stand out. Following the logic, human society by its nature must have a majority who do not stand out, and hence who - from the optic of a Tarunculus - are obliged to be failures.
Eyewash. The simple fact is that most people, by temperament, upbringing and circumstance, are not meant to be stars on the stage. If life has any meaning at all, it has meaning in obscurity. It is something emphasised more by Catholicism than perhaps any other religion. One common denominator of the saints is their preference for a humble life. The last thing they wanted was to be big shots. One reads of them going off into the desert, often permanently, to get away entirely from society. The ones who became socially significant were those who were not interested in significance but committed to doing a necessary job of reform. St Ignatius once said that if the Pope disbanded his order (the Jesuits), fifteen minutes of prayer would be enough to restore his tranquillity. He meant it too.
What is good about obscurity? Just this, that one does not sink one's heart and soul too much into human affairs. Not 'humans', just 'human affairs'. No matter how obscure a person's life is, he still has a real effect on his immediate entourage: family, friends, colleagues. They are what matter. But not being obsessed about human affairs frees the mind to look further. Aemilia gets caught up her father's dream of the restoration of Roman greatness, but eventually comes to herself and returns to her true centre of gravity, her faith in God. It's only after that that she finds her true calling, which is significant after all but not what she either looked for or expected.