Nothing gold can stay
I think the poem means it can't stay fall forever.
Nothing in fall can stay it all has to go away.The leaves dry up and go away. fall only stays for a little while.
The author is telling about how fall won't last so we need to enjoy it while it lasts.
The attitude is kinda sad because it says the gold will go away.
It is sad because fall only comes and goes.
Nothing Gold Can Stay means like the gold means leaves so no leaves can stay.When fall ends every thing goes away.
The theme is about fall every thing dries up and goes away getting ready for winter.