Until this moment, the speaker has been making lots of commanding statements. This line introduces the beloved's death into the poem. Now we know why he's been calling for quiet, and we start to understand our guy a bit better.
Let aeroplanes circle moaning overhead Scribbling on the sky the message He Is Dead. (5-6)
Here's the thing about death. People usually don't skywrite about it. Death and mourning are personal, and usually limited to a relatively small group of people. But the speaker's grief feels so huge, he wants everyone to pay attention.
I thought that love would last forever: I was wrong. (12)
The speaker's thoughts about life and love have been completely overturned by the man's death. He realizes that nothing, not even love, can withstand time. Death doesn't just snuff out life—it snuffs out love, too.
The stars are not wanted now: put out every one, Pack up the moon and dismantle the sun, Pour away the ocean and sweep up the wood; For nothing now can ever come to any good. (13-16)
The speaker's grief is so intense that he doesn't want any reminders of beauty in the world. He doesn't want to see the stars, the moon, the sun, the ocean, or the forests. That's asking a lot, to be sure, but we can understand where he's coming from. Clearly he's in the Depression Stage of grief. But hey, the next step is acceptance, so maybe there is a bit of hope.