Stanza 6 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Darkling I listen; and, for many a time
I have been half in love with easeful Death,

The stanzas in this poem actually connect seamlessly. At the end of stanza 5, the speaker moved from smells to sounds. Now he says that he is listening in the darkness.
The experience of being alone in the dark seems related to the experience of death, and he thinks maybe death wouldn't be so bad. "This is easy," he thinks. "I could get used to this."
Death would be another way to free himself of all his worldly cares. Maybe he's confusing death for sitting on a beach in Barbados….

Call'd him soft names in many a mused rhyme,
To take into the air my quiet breath;

This is turning into a love story between the speaker and death. The speaker whispers sweet nothings to death. And by whisper we mean, "writes rhyming poetry about." Yeah.
It's true: Keats was obsessed with the idea of death, and he often wrote about it.
Line 54 is mysterious: we think it means either that he wants death to take the air from his lungs, or that the air takes his breath along with his verses.

Now more than ever seems it rich to die,
To cease upon the midnight with no pain,

He's really quite taken with this death idea. While in the world of the nightingale, he thinks it would be "rich to die." Many people are afraid that death will be empty, but richness is associated with an abundance of good things, which is almost the opposite of emptiness.
He'd like to go out quietly, in the middle of the night. He'd just stop existing: "cease."
This part of the poem is kind of creepy, because Keats did die very young.

While thou art pouring forth thy soul abroad
In such an ecstasy!

He wants to die at midnight, while listening to the nightingale singing.
We were wondering what happened to the nightingale. He seems to forget about the nightingale at the beginning of the stanzas and then return to it at the end, as if he suddenly remembered: "Oh, right: this is supposed to be a poem about a bird!"
The nightingale is kind of like a poet, sending its voice into the air just as Keats sends his rhyme into the air. The bird's music expresses its "soul." Birds have souls? This one does.
The bird is completely lost in the moment of pure joy and "ecstasy."

Still wouldst thou sing, and I have ears in vain—
To thy high requiem become a sod.

He imagines what would happen after the moment of his death. Basically, the bird would keep singing as if nothing had happened.
The speaker would still have "ears," of course: or at least. his corpse would. But the ears would be useless ("vain") because there is no brain to process the sounds.
The bird would be then singing a "high requiem," a kind of church service with music sung for a dead person. Lots of classical musicians have composed amazing requiems, like Mozart, but we'd bet the nightingale probably doesn't know it is singing one.
And neither would the speaker, of course. By that point, he'd just be an inanimate object, like a piece of grassy soil or "sod."