Poetic Form of Sonnet 73

Shakespeare's Sonnet 73 follows the basic pattern of a Shakespearean Sonnet, that is three quatrains of an iambic pentameter followed by a heroic couplet. The third quatrain of Sonnet 73 reads:

In me thou see'st the glowing of such fire

That on the ashes of his youth doth lie,

As the deathbed whereon it must expire,

Consumed with that which it was nourished by.

The above quatrain is referring to a fire in the sense that fires are short lived and the speaker is comparing these fires to ones life. The speaker reminds us that life is not forever and that we will eventually become old and die. The speaker is also saying that our youth is what eventually kills us, meaning everything we do causes our death.  

The writer (Shakespeare) emphasizes his thoughts on death and life by using a particular poetic form. The rhyme scheme used is an iambic pentameter and it ends up looking like this:

ABAB CDCD EFEF GG

The GG at the end represents a heroic couplet, which in this case brings us to the conclusion that the speaker is warning someone about how he is living his life and convincing him to live life to the fullest. The rhyme scheme in Sonnet 73 creates a dramatic affect especially when talking about death and the end days. Lines like "such fire" "must expire" would not have the same meaning if the speaker had just plainly said the fire will burn out eventually.

The writers use of commas also plays a significant roll in the message of this poem. The second line of Sonnet 73 reads: "When yellow leaves, or none, or few, do hang". Without the commas this line would say something like "When only a few yellow leaves hang". Although both lines basically mean the same thing, the revised line loses a lot of emphasis and becomes quite boring to the reader. 

As in most poems, the specific poetic form of Sonnet 73 brings the poem together in a way that would not be achievable otherwise.