Helen, thy beauty is to me Like those Nicean barks of yore That gently, o'er a perfumed sea, The weary way-worn wanderer bore to his own native shore (1-5).
These lines are most likely a reference to the Roman poet Catullus. The speaker compares himself to a poet who was and is nothing short of a big deal in the history of poetry. It sounds like he is making himself seem important as a poet.
Thy hyacinth hair, thy classic face, Thy Naiad airs have brought me home (7-8)
Helen's features resemble a famous work of art. Her hair is just the right color and length, and her face is a classic. This foreshadows the final stanza, where the speaker compares Helen to a statue.
Lo, in yon brilliant window-niche How statue-like I see thee stand (11-12)
The speaker says Helen is "statue-like." This phrase suggests that she is beautiful, but also dead. A statue is a piece of stone. It isn't "alive" (it doesn't move or anything like that). Perhaps the speaker is implying that his idea of Helen is just an idea, a fantasy.
The agate lamp within thy hand! (13)
An awesome rock (agate) lamp? Sure sounds like a work of art if we ever saw one. Psyche-Helen is holding the lamp, so it seems like she's associated with art. Some scholars say Jane Stanard (i.e., Helen) first encouraged Poe to write poetry, so perhaps this is a secret little reference to her role in Poe's artistic life.