The beginning of the poem is rhythmically intense, as the speaker repeats the word "break" to create a line of three stressed syllables in a row (this repetition is an example of epizeuxis). This relentless rhythm builds a startling opening that is reminiscent of the sound of powerful waves crashing over rocks on a shoreline—the exact thing that the speaker focuses on in the first stanza, calling out to the sea and telling it to "break" upon the nearby stones.
The alliteration in this line adds to this sense of emphasis, as the /br/ sound repeats three times. Similarly, the assonance that appears in the long /a/ sound ("break") pushes the effect of this repetition even further, making it sound even more untiring. In this way, the natural world surrounding the speaker emerges right away as bleak and unforgiving.
On the whole, the speaker's use of apostrophe to address the sea not only establishes the setting of the poem (clarifying that the speaker is standing on the shoreline), but also highlights that the speaker sees the surrounding environment as quite harsh. The speaker continues in line 2 to employ bleak terms, using the words "cold" and "gray" in reference to the rocks on the shore. Along with the power of the first line, these descriptors make the scene of the poem feel hostile, as if the speaker is fixated on all the ways in which the surrounding world is cruel and inhospitable.
This interpretation is reinforced by the metrical nuances of the first two lines: after the three consecutive stresses in the first line, the poem's next stressed syllable lands on the word "cold":
Break, break, break,
On thy cold gray stones, O Sea!
"Break, Break, Break" is metrically complex, since it strays from convention in its use of rhythm. Having said that, the poem frequently employs trimeter (lines with three metrical feet), as is the case in the second line. The first metrical foot in the second line is an anapest, which is a poetic foot with two unstressed syllables followed by a stressed syllable (in this case, "On thy cold"). This places an emphasis on "cold" that ultimately expands upon the speaker's description of the environment as grim and desolate (though it's worth noting that some might argue that "thy" should receive a stress, too—either way, though, "cold" would remain stressed). Accordingly, readers are encouraged to view the immediate landscape as ruthless and severe.
At the same time, it's worth noting that this landscape has yet to be truly revealed, since the only thing readers have been told about it is that waves are breaking on "cold gray stones." As the poem continues, then, it remains to be seen whether the speaker's dreary description of this landscape is accurate, or if this bleak presentation is actually a reflection of the speaker's internal emotional state.