Duration of Soul in "Ode to a Nightingale"

To me, Keats seems here to be comparing his soul to the nightingale. When he leaves the world for where the nightingale lives, he leaves the place that causes his happiness as well as his sadness. This feels to me like he has closed his eyes and let go of material things in search of some deeper meaning. In fact, the way that the soul is treated in this poem reminds me of Descartes ("I think, therefore I am"). This is especially evident when Keats writes that the nightingale is immortal. It is easy for humans to feel that, since we have a consciousness that seems to be separable from some of the functions of our body, our soul/consciousness will live forever somehow and is more powerful than the material world, or is at least made of different stuff. What's interesting is that in this poem, Keats writes that the nightingale was present long before the writer's body, which is not how we usually think of the duration of the soul-stretching into the future, not up from the past. Perhaps what he is trying to get at here is not the duration of one soul through history but the duration of an aspect of human nature- the one that drives us to introspection and to question the nature of humanity- and the dangerous nature of heeding its call.