Although "Preludes" is presented as a single poem, it is actually a collection of short pieces that T.S. Elliot wrote while in college. "Preludes" shows his development in free verse and his changing attitudes.
The poem is divided into four parts, each with a different mood, and each following the previous to form the whole. As a whole, the mood is introspective and somewhat resigned; each part represents both the inevitability of fate and the futility of ambition, yet without directly making these emotions negative.
The first part's mood is contemplative, as the narrator watches a city move from the bustle of day into quiet night. The lines:
And now a gusty shower wraps
The grimy scraps
Of withered leaves about your feet
--are evocative of the damp, often cold streets of a city in the winter.
The second part is almost bitter; the waking man thinks about his life:
With the other masquerades
That time resumes,
One thinks of all the hands
That are raising dingy shades
In a thousand furnished rooms.
He realizes that he is just like a "thousand" other people, and has nothing unique to call his own; his existence is, at the moment, a "masquerade."
The third part is in second-person perspective, addressing the reader directly:
You dozed, and watched the night revealing
The thousand sordid images
Of which your soul was constituted;
They flickered against the ceiling.
Less depressive than the previous part, this part shows a person who can't stop thinking about his past mistakes. The mood is sombre, but relaxing; the reader may be unable to change his life, but accepts it, and now wishes only to forget the sad things.
The final part, with its coda from Elliot's viewpoint, puts all the previous parts into perspective:
His soul stretched tight across the skies
That fade behind a city block,
Assured of certain certainties,
The conscience of a blackened street
Impatient to assume the world.
The unnamed man who has suffered and lived is now part of the city and it part of him; he knows that things will happen beyond his ability to change and that he must only wait for morning, when the previous day will repeat itself. Elliot's final lines:
The notion of some infinitely gentle
Infinitely suffering thing.
--could refer to the person in the poem, or to the world itself; all life contains periods of suffering and periods of calm, and it will always recur, regardless of the circumstances.
(All Quotes: Elliot, "Preludes," bartleby.com)