This, in combination with the words "nature's changing course", creates an oxymoron: the unchanging change of nature, or the fact that the only thing that does not change is change. This line in the poem creates a shift from the mutability of the first eight lines, into the eternity of the last six.
This, coupled with the words "nature's dynamic process", produces an apparent contradiction: the unchanging transformation of nature, or the fact that the only constant is change. This line in the poem serves as a transition from the theme of impermanence to one of timelessness.