In this poem, Wordsworth's speaker stands on Westminster Bridge in the very early morning and views London. What strikes them most profoundly is the stillness and serenity of the city spread out in the sunrise. Unlike later in the day, when it will be full of traffic, crowds, and activity, right now London is lovely in its quiet. The speaker says, filled with emotion,
Ne'er saw I, never felt, a calm so deep!
The "mighty heart" of the city, they go on to say, is "lying still."
Romanticism, unlike realism, endeavors to show the world in a positive light. This poem is a Romantic treatment of London because it depicts the city at a lovely moment. Beneath the dirt, crime, and poverty of the city is a beautiful, calm heart, a soul in repose.
The treatment is Romantic, too, because the speaker responds emotionally to the early morning scene laid out before them as they view it in the hazy glow from the bridge. The exclamation mark in the quote above testifies to the speaker's heart being overwhelmed by the deep calm they see. The speaker says the "soul" that could pass by this scene without being moved would be "dull," because the vista is "touching in its majesty."
The Romantics exalted nature, and the speaker here connects the city to nature, stressing the air, the sun, the light, and the open fields around it. In this setting, London becomes for a brief moment before it awakes, part of a serene natural environment.