I find Ash Wednesday to be one of the most intriguing and curious liturgies of the year. Think about it: first we proclaim Jesus' instructions on how to fast, from the Sermon on the Mount:
When you fast, do not look gloomy like the hypocrites. They neglect their appearance, so that they may appear to others to be fasting. Amen, I say to you, they have received their reward. But when you fast, anoint your head and wash your face, so that you may not appear to be fasting, except to your Father who is hidden. And your Father who sees what is hidden will repay you.
Then, right after hearing about how we are supposed to wash our faces and hide our fasting from others, everyone puts dirt on their head and walks around all day like that.
What can this mean, that we proclaim the doctrine of Jesus and then ritually do the exact opposite? To me it can only be a ritualized form of admitting that we have not lived up to the good news offered us in Jesus Christ. We have heard the Gospel all year, haven't responded, so now we do a ritual that proclaims our failure physically. That's powerful. And that's my theory about why everyone in the world goes to Church today.