"Funeral Blues" pretty much puts it all out there in the title: this is a poem about death. Terrible, horrible, no good, very bad death. After the death of his loved one, the speaker has no joy or hope. He is completely and utterly devastated. There's no silver living in this poem, no happy endings, no smiles or songs. There's only the notion that death is the pits, and not just for the dead—for the living, too.
There is no hope at all in "Funeral Blues." As the speaker says, "nothing now can ever come to any good."
The very fact that the poem "Funeral Blues" exists provides hope. Art has been made in the wake of the man's death. Poetry is a kind of hope.
The speaker spends a whole lot of time in "Funeral Blues" issuing commands to an unnamed audience. He may be actually giving a eulogy at a funeral, or he may be talking to himself and expressing his desires. Either way, communication plays an important role in this poem, because we have all kinds of it here—private telephone communication, public skywriting, even traffic directing. "Funeral Blues" raises all kinds of questions about private and public speech, and private and public mourning. Does mourning have to be a public act? This speaker seems to think so.
Mourning is a public act. The only way for the speaker to adequately express his grief is for him to tell the world about his pain.
Mourning should be a private act. The speaker should stop trying to get the world to feel his pain.
The speaker of "Funeral Blues" wants us to put out the stars and dismantle the sun. These hyperbolic statements and the ones that follow are all about shutting down the natural world in order to demonstrate this poor guy's grief. It seems like the speaker knows that his commands are hyperbolic, exaggerated, and impossible, but thinks that nothing smaller than nature itself can communicate his despair accurately.
Nature is universal. The speaker issues his commands against nature so that everyone can understand his pain.
The speaker doesn't want nature to "end" for everyone. He just doesn't want to be reminded of the beautiful and romantic world out there while he's grieving.