The poem is about losing innocence
it means that: nature's first green is gold: which is refering to when your a child your gold her hardest hue to hold: it's hard to stay young her early leafs a flower but only so an hour: it's like being a teen young and ineceent then leaf subsides to leaf soo eden sank to grief: you become old and die (eden sank to grief) so dawn goes down to day, nothing gold can stay: you become old and plain, you aren't young forever
