Moody Modernism
Eliot, a despite being a modernist (part of the literary movement to make things "new") had some pretty strong opinions about modern life and its effects on our humanity. You could even say it's his favorite subject.
In "Preludes," our conscience has been dulled by distractions, and our minds are filled with sordid images and ideas. The culprit is our preoccupation with modern life, with its news cycle and business, all of which leave us little time to nurture our souls. Eliot's most well-known poems, like "The Waste Land" and "The Love Song for J. Alfred Prufrock", expand on the ills of modern society with similarly gloomy tones.
"Preludes," however, suggests at the end that humanity has always been gloomy and full of struggle—it just didn't used to be so preoccupied. Don't get too distracted to remember the lessons of the past, he warns in his poems; those lessons might just save our souls from decay.