«Look in thy glass, and tell the face thou viewest
Now is the time that face should form another».
Drawing on farming imagery, the poet focuses entirely on the young man’s future, with both positive and negative outcomes. However, the starting point for these possible futures is “Now,” when the youth should “form another,” that is, father a child.
Look in thy glass, and tell the face thou viewest
The sonnet begins with the image of a mirror — “Look in thy glass” — and is repeated in the phrase “Thou art thy mother’s glass.” Continuity between past, present, and future is established when the poet refers to the young man’s mother, who sees her own image in her son and what she was like during her youth, “the lovely April of her prime,” a phrase that recalls the images of spring in Sonnet 1. Likewise, the young man can experience a satisfying old age, a “golden time,” through his own children.
The negative scenario, in which the young man does not procreate, is symbolized in the poet’s many references to death. In lines 7 and 8, the poet questions how the young man can be so selfish that he would jeopardize his own immortality. The reference to death in line 14 stylistically mirrors the death imagery in the final couplets of the preceding sonnets, including the phrases “the grave and thee” in Sonnet 1 and “thou feel’st it cold” in Sonnet 2.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com