Look in thy glass and tell the face thou viewest
Now is the time that face should form another;
Whose fresh repair if now thou not renewest
Thou dost beguile the world, unbless some mother
For where is she so fair whose uneared womb
Disdains the tillage of thy husbandry?
Or who is he so fond will be the tomb
Of his self-love, to stop posterity?
Thou art thy mother's glass and she in thee
Calls back the lovely April of her prime;
So thou through windows of thine age shalt see
Despite of wrinkles, this thy golden time
But if thou live, remembered not to be
Die single and thine image dies with thee
Even though he will grow old and wrinkled — seeing his future self as if through a window — he will see his loveliest youth by simply looking at his child. Youth is often seen as the best age of a man’s life, in  King Richard III , Shakespeare writes of; 
 …the golden prime of this sweet prince…" 
 The first three quatrains end with the  volta  or “turn”, forming a pause or  caesura . Thre remaining couplet will form a resolution.
Sonnet 3