How do lines 6-7 of Robert Frost's poem Nothing Gold Can Stay, contribute to the development of a theme in the poem?

Line 6: "So Eden sank to grief,"

Line 7: "So dawn goes down to day."

Explanation: The theme of this poem is that nothing gold can stay, or nothing pure and innocent lasts. Line 6 recalls how Eden was once a pure and perfect place, but eventually became exactly the opposite due to Eve eating the forbidden fruit. Line 7 mentions how the day begins pure with the sun rising at dawn, but as the day progresses, purity and innocence are corrupted in the world by the actions of mankind.