What Am I Riddles

What is the longest and yet shortest thing in the world, the swiftest and yet the slowest, the most divisible and the most extended, the least valued and the most regretted, without which nothing can be done, which devours everything, however small, and yet opens the life and spirit to every object, however great?

I have a name, but it isn’t my name. My face shows signs of age. I always mean the same thing, no matter what I say. I’m born in mourning, and I last ’til the end of days. Men plant me, but I never grow. They run from me, but I never move. They look at me and see their future, rotting in the fields where I bloom. What am I?