Shakespeare's Sonnet 68

Thus is his cheek the map of days outworn,When beauty lived and died as flowers do now,Before these bastard signs of fair were born,Or durst inhabit on a living brow;Before the golden tresses of the dead,The right of sepulchres, were shorn away,To live a second life on second head;Ere beauty’s dead fleece made another gay:In him those holy antique hours are seen,Without all ornament, itself and true,Making no summer of another’s green,Robbing no old to dress his beauty new;And him as for a map doth Nature store,To show false Art what beauty was of yore.

His face shows what those long-gone days were like. Beauty then lived and died as flowers do now. These false signs of beauty had not yet been invented, or dared to appear on a living face. The golden hair of the dead still belonged in their graves. It had not been cut off to live a second life on someone else’s head. Dead beauty’s hair did not yet make another person lovely.
Those pure old days can be seen in him. His beauty is real, true to itself, and free of decoration. He makes no summer from someone else’s greenery. He robs no old beauty to give his own a new look.
Nature keeps him as a model, to show false art what beauty used to be.