"Remember, man, thou art dust and unto dust thou shalt return." Memento, homo, quia pulvis es et in pulverem reverteris. This warning, from the Catholic liturgy for Ash Wednesday, is based on Genesis 3, 19: In sudore vultus tui vesceris pane, donec revertaris in terram de qua sumptus es: quia pulvis es et in pulverem reverteris.
How real can we and this world be if in a little while we all will be nothing but dust and ashes?
The typical secularist is a reality denier who hides from the unalterable facts of death and impermanence. This is shown by his self-deceptive behavior: he lives as if he will live forever and as if his projects are ultimately meaningful even though he knows that he won't and that they aren't. If he were to face reality he would have to be a nihilist. That he isn't shows that he is fooling himself.