We don't know the speaker's name, age, or even gender. (Most people assume it's a he and that Coleridge himself has assumed the role.) We do know, though, that the speaker cares very deeply about nature.
In the first stanza, he invites two friends to sit with him and muse about the night sky. As they do so, a nightingale sings, which prompts the speaker to make his feelings known about how poets have treated this famous bird.
They characterize it unfairly, he says, based on their emotions. This musing leads to a lengthier discussion on enjoying nature and youth. Just think of him as a man with a message.
The message? We should revel in nature, rather than try to shape it to fit our poems or moods. And he's no hypocrite. He reveals that he is raising his son to appreciate the night sky, and hopes that others will learn to do so, too.