Can you please tell me what the poet is saying in these lines from "Ode to a Nightingale"?
Thou wast not born for death, immortal Bird! No hungry generations tread thee down; The voice I hear this passing night was heard In ancient days by emperor and clown: Perhaps the self-same song that found a path 65 Through the sad heart of Ruth, when, sick for home, She stood in tears amid the alien corn; The same that ofttimes hath Charm'd magic casements, opening on the foam Of perilous seas, in faery lands forlorn
Keats is stating that, in his opinion, nightingales have been alive and present throughout human history. "Thou wast not born for death, immortal Bird!" He is supporting this opinion with various theories or demonstrations of a nightingale's presence at places and times in the past.
Keats suggests that the call of a nightingale was heard "in ancient days by emperor," implying that nightingales had lived in the Roman Empire and other long-ago empires.
He refers to Ruth, the Biblical Moabite widow who follows her widowed mother-in-law back to the mother-in-law's homeland near Bethlehem, harvests "the alien corn" from the fields to allow them to live, and eventually remarries and becomes the great-grandmother of King David, the greatest of the Israelite kings.
Keats places the call of the nightingale throughout the world of fantasy, referring to "magic casements" and "faery lands."