Remember that you are dust and to dust you shall return goes the declaration of Ash Wednesday. The imposition of ashes is a memento mori — a reminder of mortality. On this day people are given the stark reminder of the end of all humanity: dust and the grave. This being true then what?
This the whole point of religion. What do you do with death? How do you respond to the ending of your existence? Christianity says this is not the end if one accepts the radical gift of grace in Christ Jesus. But this radical gift is truly radical — it goes to the very root to things. We will be saved out of our death not our success. Remember that you are dust — a memento mori.