I said over on Meditation Matters that Ash Wednesday is an acknowledgement of impermanence. In a way, so is the whole duration of Lent.
Here is a poem about just that:
If we do not learn to bow to mystery, our inner deprivation will be very, very great -- of that I am convinced.
The Wish to Be Generous
All that I serve will die, all my delights,
the flesh kindled from my flesh, garden and field,
the silent lilies standing in the woods,
the woods, the hill, the whole earth, all
will burn in man's evil, or dwindle
in its own age. Let the world bring on me
the sleep of darkness without stars, so I may know
my little light taken from me into the seed
of the beginning and the end, so I may bow
to mystery, and take my stand on the earth
like a tree in a field, passing without haste
or regret toward what will be, my life
a patient willing descent into the grass.