In a few minutes, I will put ashes on your foreheads, and I will say the words, “Remember that you are dust, and to dust you shall return.” What does that mean? Well, our first thoughts are of the body. This life on this earth is temporal and will pass away. Without the teachings of Christ in our hearts, this is a very bleak philosophy, almost Buddhist: this life ends and then afterwards is nothingness.
I knew a woman who would just sit at her desk and rub off lottery scratch tickets. I questioned why she wasted so much money. She told me that life was short. When she discovered she had cancer, she locked herself in her house and never came out again until she died. She had given up. This life was all there was.
The Christian believes in everlasting life. The Christian believes in a body AND a soul. Our flesh may become dust, ashes, but our souls live on. At judgment day, we will be given new bodies that do not decay and do not go to dust.
Another, deeper meaning of these words is that the world is headed for ashes. The world is passing away, and heaven is the only thing imperishable, so investing in this world is a mistake. We will find that we have invested in nothing. Saving up our treasures in heaven allows us to invest in the thing that will not become ashes.
At judgment day the earth is restored and heaven and earth combine. In other words, shoot for the earth and you lose both heaven and earth. Shoot for heaven and you get both. Feed the flesh and you lose both flesh and soul. Feed the soul, and you get both flesh and soul in the end.
Remember, you are but dust. Also remember: you are immortal.