How does the structure of "The Lake Isle of Innisfree" contribute to the poem's meaning?

The structure of W. B. Yeats's "The Lake Isle of Innisfree" mimics the way the water laps at the shores of Innisfree—a sound that's stuck not just in the speaker's head but in his heart, too. Here's how Yeats turns verse into lake water.
The poem is made up of three quatrains—or stanzas four lines in length—that follow an alternating rhyme scheme. In the first stanza, Lines 1 and 3 rhyme with each other, and Lines 2 and 4 rhyme with each other. In the second stanza, Lines 5 and 7 rhyme with each other, and Lines 6 and 8 rhyme with each other, and so on.
Now let's talk about the beat. The first three lines in each stanza are in hexameter, which means they have six stressed syllables apiece. The last line of each stanza is in tetrameter, which means they each have four stressed syllables. All the lines in "The Lake of Isle of Innisfree" have a rolling, sing-song quality to them. Rhythmically, it's not totally iambic hexameter and tetrameter from start to finish, but it's close.
The effect? A measured yet lolling cadence that replicates the sound of waves advancing and retreating from the lakeshore, just like the ones the speaker hears even if he's in the middle of traffic.