Those hours that with gentle work did frame
The lovely gaze where every eye doth dwell,
Will play the tyrants to the very same
And that unfair which fairly doth excel:
For never-resting time leads summer on
To hideous winter, and confounds him there,
Sap checked with frost and lusty leaves quite gone,
Beauty o'er-snowed and bareness everywhere.
Then were not summer's distillation left
A liquid pris'ner pent in walls of glass,
Beauty's effect with beauty were bereft,
Nor it nor no remembrance what it was. But flowers distilled, though they with winter meet, Leese but their show, their substance still lives sweet.
It repeats the emphasis on human aging, compared with progress of the seasons. The “howers,” with which Sonnet 5, the first of a pair of sonnets, opens are the classical ‘Hours,’ the Horae or ‘Ωραι, daughters of Zeus and Themis, who presided over the seasons – hora can also mean ‘season’ – and their products were thought to engender ripeness in nature and the prime of human life. But the hours, which created his look, will in time act as destructive tyrants and make “vnfaire” that which in its fairness excels.
The final couplet about "distilled flowers" refers to the extraction of perfume from petals, in which the visible "show" of the flowers disappears, but their "essence" remains. The same distillatory trope recurs in Sonnet 54, Sonnet 74 and Sonnet 119. The reference is probably to the Youth's "seed" - his capacity to prolong his "essence" by producing children, but it is also an example of Shakespeare's play on the question of what is transient and what eternal in the material world.