"Prufrock" gives a picture of modern life as a disconnected, somewhat despairing, existential ramble. Modern life is alienation, and petty alienation at that.
To illustrate that a bit, look at how much hesitation and back and forth there is in the poem. Look at how the narrator frets over things. They talk, but they reach no conclusion. He walks through the streets, but there isn't a sense of being part of a unified community. Instead, it's a world of fog and indecision. Look at how the narrator frets over his lack of daring, over growing old, and ultimately over small things like eating a peach. It is a life, as the poem says, measured "with coffee spoons." There is no connection with the divine or the supernatural; think of how the mermaids sing, but not for the narrator.