The full poem is here:
O what purpose, April, do you return again?
Beauty is not enough.
You can no longer quiet me with the redness
Of little leaves opening stickily.
I know what I know.
The sun is hot on my neck as I observe
The spikes of the crocus.
The smell of the earth is good.
It is apparent that there is no death.
But what does that signify?
Not only under ground are the brains of men
Eaten by maggots.
Life in itself
An empty cup, a flight of uncarpeted stairs.
It is not enough that yearly, down this hill,
Comes like an idiot, babbling and strewing flowers.
More information is available here http://en.wikipedia.org/wiki/Edna_St._Vincent_Millay.