A young worker experiences a feeling of profound dissatisfaction with his life:

the quiet of non-hope.
To believe mankind lost and to have no desire to do anything to the contrary, no desire to lose myself, for instance, along with it

.
This dissatisfaction («these abstract furies») is an intimate matter, but also an awareness of cosmic grief.
The young man seeks to escape it through a journey that might constitute both a return to his childhood and, at the same time, an exploration of self, a reflection upon the prevailing values and ideas in society.
The journey is structured around several key moments: the acquaintances made on the train, where people are archetypes of social roles; the arrival in the village; the conversation with his mother; the rounds made with his mother among the village houses to administer injections; the encounter with the knife-grinder and the drunken bout in the tavern; the brother killed in the war; and finally «the synthesis» of the entire novel by the village's bronze monument.
The development of the themes, the frequent shifts in style and narrative rhythm (at times cinematic, at others lyrical and evocative, rich in symbolism and allegory) make it extremely difficult to provide a single, definitive interpretation, as demonstrated by the critical reception, where each commentator seems to be discussing a novel entirely different from the one read by the others.
There are undoubtedly several interpretive keys: the relationship with parents and the native land, the depiction of a crisis of values that finds no answer in political and social forces (personified in the knife-grinder, the upholsterer, and the innkeeper), existential despair, which is not resolved by a return to the maternal womb, and a stylistic search for a cinematic approach to writing.
It is probable that the novel is a bit of all of this, so much so that it takes the shape of an open and dynamic system that cannot be enclosed within a single interpretation.
I like to think that the true interpretive key to the novel is the context, that Sicily,

a small, huddled Sicily, of medlars and roof tiles, of holes in the rock, of black earth, of goats, with a music of reproaches, receding behind us, and turning into cloud and snow, high above

.
That setting which frames the continuous rhythm of life («the round of injections»), of illness and death, which make all men alike and equal before suffering and a common destiny.

It was night over Sicily and the calm earth: the outraged world was covered in darkness, men had lamps beside them shut up with them in the rooms, and the dead, all the slain, had sat up in their graves, meditating.
I thought, and the great night within me was night upon night.
Those lamps below, above, and that cold in the darkness, that ice of star in the sky, were not a single night, they were infinite; and I thought of my grandfather’s nights, my father’s nights, and the nights of Noah; the nights of man, naked in wine and defenseless, humiliated, less a man than a child or a dead man

.
And so the true theme is, perhaps, identification and the sense of belonging to a collective dimension, constituted by humankind.
The central character is that of the Great Lombard, who feels and expresses a yearning for great duties, to do something for humanity.
Yet no one knows what to do, and so the worker concludes:

I do not weep within myself.
I do not weep in this world...
And he walked out of the house, on tiptoe

.
The novel features deeply evocative pages and reaches its stylistic and narrative peak in «the round of injections» and more generally in the first part: the train journey and the arrival at the village.
At other times an intellectualistic approach prevails, which also leads to a fragmentation of the narrative, rendering it at times redundant and prolix.

Conversation in Sicily