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?
A refusal to recreate the youthful condition of his face is seen as betraying an obligation to the world, which recalls  the final line of Sonnet 1 .
Sonnet 3