His fascination with dreams and what is communicated to us through dreams is a theme that is often woven through many of his work. He would be pleased that this poem has resonated in many different ways with the commentators below- a sign, I think, of his greatness.
I think he speaks of a lighthouse guiding him through the storm the lighthouse his lover of course who haunts him in his dreams the place where a lonely spirit roams an the day star the sun awakening him in the morning his joy departed.
Poe reveals that he has been numbed by pain in his life-to the effect that he feels he is in a state between waking and sleeping ('waking dream of life and light hath left me broken hearted') .
But it isn't just pain. There was something good in his past. He explains that in addition, he chooses to focus on whatever was good in the past (he later refers to this as 'that holy dream', 'lovely beam', 'light trembled from afar') . To the extent that he relegates his real life to the reality level of a dream ('What is not a dream by day') .
He acknowledges this fixation on the past might just be a dim flicker of hope (light trembled from afar) for his current state (thro' storm and night) . But then, it is what cheered him (third stanza) -and more importantly, it is the only thing with him (lonely spirit guiding) -he concludes by asking what else might have possibly helped him more?
The last line is a statement of hope, hiding a note of desperation (there is no help Poe can think of, other than his memories) .