The poem is about personally inflicted pain due to loss of love (like a breakup) "is there a balm in Gilead?" is actually a Bible reference, Gilead is a part of modern day Jordan, known for it's healing ointment. The narrator is really asking if there is any healing. The narrator continually asks dark questions of the raven fully knowing that the answer is always, "nevermore" therefore inflicting a sort of mental torture. Some people cut themselves, this guy asks birds what they think. (not putting down self harmers, I'm one myself)
The main idea is more specific than a theme . The theme could be food and the main idea might be that people need to be more careful about what they eat . Hope that helped
