As far as I can tell in Kaleb Christenberry's poem, "The Last Sonnet," the themes seem to reflect a student's difficulty in writing a sonnet, which is his last, and how he wishes he could avoid it.
In a general sense, perhaps the poem reflects any desire to be relieved of completing a task that we wish we did not have to do. In this case, it is a sonnet. Literally speaking, it could be going to the dentist or taking out the trash.
However, I find that the poem is so "inferior" to the beautiful work of authors like Shakespeare (who wrote so many lovely sonnets), as well as Wordsworth, Wyatt and Milton (among others), that I can only conclude that this poem is poking fun at the sonnets youngsters may be forced to write for classroom assignments. If this is the case, Christenberry has done a fine job: the sonnet sounds like something a sixth-grader would write (not to insult the student). Personally, I find the poem to be choppy, non-musical, awkward, and unappealing.
For example, "listen" to a few lines from Shakespeare's Sonnet 29:
When, in disgrace with fortune and men's eyes,
I all alone beweep my outcast state
And trouble deaf heaven with my bootless cries
And look upon myself and curse my fate...
There is a musical rhythm here; the words are chosen carefully, and the reader flows from one line to the next, effortlessly. The rhyme found at the end of each line forms a pattern as well: a-b-a-b. "Eyes" and "cries" rhyme, and "state" and "fate."
Compare Shakespeare's work with Christenberry's. The rhyme at the end of the first and third line is what I call "cheap rhyme." It is rhyming so it the line endings have similar sounds, but there is no serious attempt to provide a flow or a more "artful" word, or a rich content:
There are many challenges that I have seen...
to this challenge I am not very keen...
My overall sense, then, is that the author is poking fun at the deadly sonnets some students write to fulfill an assignment, where meeting the rhyme scheme and number of syllables per line is like a "Mad Lib," where any number of words can be paired that make no sense. Perhaps Christenberry is drawing our attention to the artistry true poets employ because they have a sense of poetry within. For the student who struggles just to finish—rhyming words like "assignment" and "alignment"—he may rest assured that his teacher is also struggling with his poem. And that may well be the author's point. For some people, writing poetry is a useless exercise, and a painful journey for the reader.
If this is the case, the author has provided an excellent example of poetry written under duress rather than one written with passion and fire.