Being reminded that you shall simply return to dust seems to me to be at odds with most popular Christian thought. Without the promise of eternal life what are we left with? I would like to think this has something to do with Christ's purported contact with Buddhist thought during the 18 years of his life not mentioned in the Bible but even Buddhism promises some sort of rebirth. This might be heresy but the rites of Ash Wednesday remind me more of something one of my personal saints said:
Memento homo, quia pulvis es, et in pulverem reverteris.
(Remember, O man, that you are dust, and unto dust you shall return.)
I would love to believe that when I die I will live again, that some thinking, feeling, remembering part of me will continue. But much as I want to believe that, and despite the ancient and worldwide cultural traditions that assert an afterlife, I know of nothing to suggest that it is more than wishful thinking . . . The world is so exquisite with so much love and moral depth, that there is no reason to deceive ourselves with pretty stories for which there's little good evidence. Far better it seems to me, in our vulnerability, is to look death in the eye and to be grateful every day for the brief but magnificent opportunity that life provides.—Carl Sagan
Here Mr. Billions-and-Billions describes how it's a little bit more than dust from whence we came (skip to 2:30 if you're in a hurry):