What is the impact of the bird's song on the poet in "Ode To Nightingale?"

The poet admires the nightingale's song because the bird sings with "full-throated ease." The poet recognizes a freedom of creativity and art in the song. In the third stanza, the poet notes that the nightingale does not have the concerns that he, a human being, has:

Fade far away, dissolve, and quite forget
What thou among the leaves hast never known,
The weariness, the fever, and the fret
Here, where men sit and hear each other groan;

The nightingale's song is beautiful and the poet recognizes the creativity of that song as something comparable to his art of poetry. So, he sees a common connection there. But the poet is particularly fascinated because the song comes from a creature who is not burdened by the realities of aging, sorrow, and death. To the poet, the nightingale sings without those concerns. He, on the other hand, writes poetry with those concerns always in mind. Keats was always too aware of his own mortality. And as an artist trying to create poetry that could be timelessly celebrated, he is thinking of immortality. He sees/hears that immortality in the nightingale's song because the song comes from a place in which mortality is not a concern:

Thou wast not born for death, immortal Bird!
No hungry generations tread thee down;

The poet wonders what it's like to sing/create without those concerns. He also longs for his own poetry to achieve the kind of immortality he hears in the nightingale's song.