Sonnet 6 continues the winter imagery from the previous sonnet and furthers the procreation theme. Winter, symbolizing old age, and summer, symbolizing youth, are diametrically opposed.
The poet begs the young man not to die childless — "ere thou be distill'd" — without first making "sweet some vial." Here, "distill'd" recalls the summer flowers from Sonnet 5; "vial," referring to the bottle in which perfume is kept, is an image for a woman whom the young man will sexually love, but "vial" can also refer to the child of that sexual union. Ten children, the poet declares, will generate ten times the image of their father and ten times the happiness of only one child.
The poet strongly condemns the young man's narcissism in this sonnet by linking it with death. "Self-killed" refers both to the youth's hoarding his beauty by not passing it on to a child, and to his inevitably dying alone if he continues his narcissistic behavior. The poet argues that procreation ensures life after death; losing your identity in death does not necessarily mean the loss of life so long as you have procreated. Lines 5 and 6 make this concept clear: "That use is not forbidden usury / Which happies those that pay the willing loan." Once you recognize the wealth of beauty by loving another person, you must use this knowledge of love if it is to increase and not decay.
Sonnet 6 is notable for the ingenious multiplying of conceits and especially for the concluding pun on a legal will in the final couplet: "Be not self-willed, for thou art much too fair / To be death's conquest and make worms thine heir." Here, as earlier in the sonnet, the poet juxtaposes the themes of narcissism and death. "Self-willed" echoes line 4's "self-killed," and the worms that destroy the young man's dead body will be his only heirs should he die without begetting a child.