Significance of the word nevermore The Raven- Edgar Allan Poe?

The raven uses the word "nevermore" a total of six times in this poem:
1. Once when the narrator asks the raven its name. I believe this means that the raven is an omen, a forerunner of fate. He has come to tell that something will occur "nevermore": "'Tell me what thy lordly name is on the Night's Plutonian shore!' Quoth the raven, 'Nevermore'".
2. Once when the narrator tries to assure himself that the raven is just a bird, and will fly away soon. I think this means that the raven and the doom and despair it brings are here to stay: "On the morrow he will leave me, as my Hopes have flown before.' Quoth the raven, 'Nevermore'".
3. Once when the narrator asks the raven for relief from his painful memories of his lost love, Lenore. This is the raven quashing the narrator's hopes of them being together again: "Quaff, oh quaff this kind nepenthe and forget this lost Lenore!' Quoth the raven, 'Nevermore'".
4. Once when the narrator asks the raven if there is "balm in Gilead"--I believe Gilead is supposed to be heaven, and balm is a kind of relief. Again, the despair is here to stay: "'Is there--is there balm in Gilead?--tell me--tell me, I implore!' Quoth the raven, 'Nevermore'".
5. Once when the narrator asks if, in a place called Aidenn (Heaven, I believe), he will hold Lenore again: "'Tell this soul with sorrow laden if,...it shall clasp a...rare and radiant maiden whom the angels name Lenore.' Quoth the raven, 'Nevermore'".
6. Once when the narrator requests that the raven leave: "'Take thy beak from out my heart, and take thy form from off my door!' Quoth the raven, 'Nevermore'".