What is the effect of the volta in this sonnet?

Question

anonymous · Answer

Sonnet 2
by William Shakespeare

When forty winters shall besiege thy brow, 
And dig deep trenches in thy beauty's field, 
Thy youth's proud livery, so gazed on now, 
Will be a tatter'd weed, of small worth held: 

Then being ask'd where all thy beauty lies, 
Where all the treasure of thy lusty days, 
To say, within thine own deep-sunken eyes, 
Were an all-eating shame and thriftless praise. 

How much more praise deserved thy beauty's use, 
If thou couldst answer 'This fair child of mine 
Shall sum my count and make my old excuse,' 
Proving his beauty by succession thine!

thebadyboy · Answer

u should put this in literature lol