Things are happening much grander and faster by this point in the poem. Nature losing its greenness triggers Frost to put a religious spin on this poem, forcing readers to parallel the fall of humanity with the loss of the green of Eden.

Nothing pure can last.

This second line ends with an end stop and finishes the sentiments that the first line and enjambment (a line in poetry that doesn’t end with a hard stop like a period) starts. "Nature” is officially personified as a "her,” which is typical for Mother Nature. And it is solidified that the greenest is the most difficult color for nature to hold, just like youth, etc. This line also has heavy alliteration with all but one word beginning with an h.

The key to understanding this poem is to think about the duplicity of words. If “Nature’s first green is gold," the reader knows that from a literal sense, "nature” isn’t described as just a single color; it’s countless colors. "First green” is spring, but it’s also youth, innocence, pureness, and other good but fleeting things. These things are subject to change, as this line suggests, with the usage of "first.”