Alexander Pope's _An Essay on Man_

This light and darkness in our chaos join'd,
What shall divide?  The God within the mind.
Extremes in Nature equal ends produce,
In Man they join to some mysterious use;
Tho' each by turns the other's bound invade,
As, in some well-wrought picture, light and shade,
And oft so mix, the diff'rence is too nice
Where ends the Virtue, or begins the Vice.
Fools! who from hence into the notion fall,
that Vice or Virtue there is none at all.
If white and black blend, soften, and unite
A thousand ways, is there no black or white?