I'll admit I don't know much about this poem: the origin, namely, or history. I assume, by its presence in Don Quixote, it to have been written by Cervantes, sort of ad hoc in service of the story, the context it appears in...
The form is - and I can't say I've seen this done often contemporarily - an "echo poem" (according to Hollander's Rhyme's Reason). Probably part of the reason it's rarely written - because the form itself has so much potential for being wonderful - is because today's editors (outside of specifically pro-meter journals) are ideologically opposed to verse forms (or received forms, tradition), somehow believing vers libre is STILL avant garde (after what? 1.5 centuries...), or somehow "more democratic," or less constraining; this, of course, refers to the American scene only, where dumbing-down is often considered both virtuous and disdainful, often unknowingly in the same mind.
Here's the poem - I don't believe any laws are being broken republishing something 500 years old...
What makes my quest of happiness seem vain?
What bids me to abandon hope of ease?
What holds my heart in anguish of suspense?
If that be so, then for my grief
Where shall I turn to seek relief,
When hope on every side lies slain
By Absence, Jealousies, Disdain?
What the prime cause of all my woe doth prove?
What at my glory ever looks askance?
Whence is permission to afflict me given?
If that be so, I but await
The stroke of a resistless fate,
Since, working for my woe, these three,
Love, Chance and Heaven, in league I see.
What must I do to find a remedy?
What is the lure for love when coy and strange?
What, if all fail, will cure the heart of sadness?
If that be so, it is but folly
To seek a cure for melancholy:
Ask where it lies; the answer saith
In Change, in Madness, or in Death.
-- To me, this poem epitomizes the essential qualities of poetry, or rather, the state it describes is the state of wonder induced by great music, powerful paintings; the serenity of detachment, a sort of free fall into grace (if I may wax poetic). Rather than re-state or paraphrase, I'd like to just present that poem as exemplary. There's music - and Quixote liberally (but regularly) moves between stanzaic AABB quatrains and echoes - and the content itself is pure unknowing, pure possibility.
Interesting to me that within this episodic, tragicomic novel (said to be one of the earliest examples of that form, the extended prose narrative) I'd find (discover, or simply stumble upon, come across) what I consider a great, great poem.