The first four lines of "Harlem Shadows" set the scene for the rest of the poem. The speaker appeals to readers' eyes and ears through imagery, detailing the sound of "halting" footsteps and the shadowy sight of dark city streets. The word "halting" hints at a feeling of uncertainty, as if the "lass" (an old-fashioned word used to describe a young woman) that the speaker mentions is apprehensive as she makes her way through the darkness.
In lines 3 and 4, the speaker further clarifies the poem's setting by saying, "I see the shapes of girls who pass / To bend and barter at desire's call." This reveals that the women surrounding the speaker are sex workers and that they're "bend[ing]" to talk to potential clients, who most likely have stopped in their cars and rolled their windows down.
Instead of focusing on the male customers, the speaker personifies "desire." This suggests that the sex workers are dealing with pure lust—their interactions with the men aren't like normal exchanges with other human beings, since the men have been overtaken by desire itself. Driven by their sexual urges, the men try to "barter" with the women, treating them like things to be bought.
In this way, the beginning of the poem presents sex work quite unfavorably, implying that the occupation has forced these women to "bend" (or submit) to men who don't actually care about them. The opening lines also establish that the poem takes place in New York City in the predominantly Black neighborhood of Harlem. This alerts readers to the racial dynamics at play in this environment.
The poem is musical and rhythmic in these opening lines as well. Take the clear, breathless alliteration of the /h/ sound in "I hear the halting footsteps of a lass / in Negro Harlem," and also note the consonant /t/, /l/, and /s/ sounds that infuse these lines:
I hear the halting footsteps of a lass
In Negro Harlem when the night lets fall
Its veil. [...]
The sibilance here reflects the hushed nighttime atmosphere, while the percussive /t/ cuts through these lines and subtly evokes click-clacking sound of footsteps against the sidewalk.
These lines also feature iambic pentameter, meaning that each line contains five metrical feet consisting of an unstressed syllable followed by a stressed syllable. The first line, for instance, scans like this:
I hear | the halt- | ing foot- | steps of | a lass
This line features a metrical substitution, since the speaker uses a trochee (stressed-unstressed) in the fourth foot: "steps of." Still, the steady da-DUM da-DUM thump of iambic pentameter defines the rhythm of the poem's opening line. This effect matches the subject, since the rhythm mimics the sound of the woman's footsteps on the sidewalk as she passes the speaker.