I see Viktoria has better information. This is what I found. I'll delete the other post.
It's on a lot of different gravestone markers, various versions and forms. I don't think it has an author associated with it.
"The original of this epitaph appeared in a European monastery. It has been oft copied and rewritten. The author seems to find it in nearly every cemetery he has visited. Readers of the Epitaph Browser send it to me more than any other inscription, each believing the sentiment unique. This page consists of many variations upon a theme"http://www.alsirat.com/epitaphs/passing.html
The Rose is red: Ye grass is green
The days are past which I have seen
As you are now so once was I but
as I am now so shall be ye
Be prepare for death and follow me.
Kind frineds beware as you pass by,
As you are now so once was I;
As I am now so you must be.
Prepare, therefore to follow me.
~on the headstone of Catherine, wife of Lawrence Hartnett, died 02/26/1883, aged 56 years, Roman Catholic Cemetery of Holmdel, New Jerseyhttp://www.atlanticmedical.net/genealogy/holmdelcatholic.htm
O' come and see this lonely place
All tho you cannot see my face
This land of darkness & of night
Here I'm concealed from your sight.
Remember me as you draw nigh,
As you are now, so once was I;
As I am now, so you must be
Prepare for death & follow me.http://www.gendex.com/users/pthree/ss%20cemetery.html
Stranger stop and cast an eye,
as you are now, so once was I.
As I am now, so you will be.
Prepare for death and follow me." http://blacksheep.rootsweb.com/2000peep.html
YOU LIVING FRIENDS, AS YOU PASS BY,
AS YOU ARE HERE NOW SO ONCE WAS I
AS I AM NOW, AS YOU MUST BE,
PREPARE FOR DEATH AND FOLLOW ME.http://freepages.genealogy.rootsweb.com/~langolier/hooper.html
...as one gravestone noted: As I am now, you shall be too! http://www.heritageinterp.com/gravesto.htm
Herb speaks to us; by his great ego we're led;
Let not your heart become reanimated.
I'm in the grave, and soon you shall be too;
I'm in the grave, and soon you shall be too.http://www.herbertwarmstrong.com/gycg/herbspeakstous.htm"Real generosity toward the future lies in giving all to the present."~Albert Camus.