How does the stucture of the poem emphasize its central ideas?

Tithonus, the speaker in this poem by Lord Tennyson, is addressing Aurora, the goddess who has both blessed and cursed him with immortality ("immortal age beside immortal youth"). The structure of the poem supports the fact that it is, effectively, a monologue spoken by Tithonus that receives no reply. Tennyson uses iambic pentameter, the meter most commonly used by Shakespeare, which creates a sense that we are listening to Tithonus as an actor on a stage declaiming a series of soliloquies. The verse is largely blank verse—that is, there is no regular rhyme scheme—which adds to the sense that it is a genuine reflection of speech rather than a poem crafted to reflect Tithonus's anguish. The steady, languid, repetitive rhythm of the poem reflects Tithonus's steady, repetitive, anguished onward plodding, the "wheel" of his existence ceaselessly turning.
The stanzas are also of irregular length, with some being very short. This stanza, for example, stands isolated:

Lo! ever thus thou growest beautiful
In silence, then before thine answer given
Departest, and thy tears are on my cheek.

It is followed by a second brief stanza—before the speaker resumes his lengthy monologue. The effect of these short stanzas, combined with the iambic pentameter redolent of dramatic monologue, is that we can imagine Tithonus pausing as if to await answer. The break between the stanzas represents the "silence" in which Aurora "growest beautiful," but she gives no answer to Tithonus's plea. Instead, she departs, leaving him to wander the earth forever, only pausing in his lamentations to listen for a reprieve which will not come.