When forty winters shall besiege thy brow,
And dig deep trenches in thy beauty's field,
Thy youth's proud livery so gaz'd on now,
Will be a totter'd weed of small worth held:
Then being asked, 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 deserv'd 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!
His beauty would be more praised if he could show his children as heirs who’ll perpetuate his beauty, so that he will renew himself in his children. 
 The first three quatrains end with an exclamation mark and the  volta  forming a pause or  caesura . The solution to the ravages of time is, for Shakespeare, procreation — “This fair child of mine”.  The beauty of the fair youth will be passed on, “by succession”.  Therefore, both father and son will be deemed beautiful. 
 The final couplet forms a conclusion and resolution; a gloomy focus on age and death rather than youth.
Sonnet 2