I want to know what the poet is saying here?
Darkling I listen; and, for many a time I have been half in love with easeful Death, Call'd him soft names in many a musèd rhyme, To take into the air my quiet breath; Now more than ever seems it rich to die, 55 To cease upon the midnight with no pain, While thou art pouring forth thy soul abroad In such an ecstasy! Still wouldst thou sing, and I have ears in vain— To thy high requiem become a sod. 60
At the beginning of his "Ode to a Nightingale," the speaker (Keats) says that he would like to escape from the world of reality. He wishes he could get drunk but, since he has nothing alcoholic available, he decides to use his own imagination to achieve that escape. He actually manages to do so, and he describes the world of the nightingale as he imagines it.
Now he has two alternatives. He can return to the world of reality, or he can remain in the imaginary world of the nightingale, which is tantamount to dying, since he could not survive there with nothing to eat or drink. He is thinking about death in the lines you have quoted. He believes it would be a desirable state, at least for him, since he has tuberculosis and does not expect to live long anyway. This seems like an appropriate moment to die, while he is listening to the nightingale singing as if it is pouring out its soul. He imagines himself dead, turned into dirt, or a sod, and imagines the immortal nightingale still singing a requiem (church music for the dead) over his grave.
It was Keats' morbid thoughts about his own anticipated death that made him want to get drunk or do anything to escape from reality so that he would not have to think such thoughts, at least for awhile. Throughout the poem there is an implicit contrast between the immortality of the nightingale and the mortality of the poet.
The immortality of the bird is a poetic conceit. Nightingales always look the same and sing the same song, so it is easy to think of this one bird as being the same one that has lived since biblical times. Keats knew nothing about evolution, the Book of Ruth in the Old Testament was about as far back as he could imagine the past extending. That is why he says that the nightingale's song is
Perhaps the self-same song that found a path
Through the sad heart of Ruth, when, sick for home,
She stood in tears amid the alien corn...
"Ode to a Nightingale" is Keats's best poem and considered one of the greatest poems in the English language.