Are They Shadows That We See?

Are they shadows that we see?
And can shadows pleasure give?
Pleasures only shadows be
Cast by bodies we conceive,
And are made the things we deem,
In those figures which they seem.
But these pleasures vanish fast,
Which by shadows are exprest:
Pleasures are not, if they last,
In their passing, is their best.
Glory is most bright and gay
In a flash, and so away.
Feed apace then greedy eyes
On the wonder you behold.
Take it sudden as it flies
Though you yake it not to hold:
When your eyes have done their part,
Thought must length it in the heart.