September 11, 2001. For those who were alive and old enough to remember, it is a day indelibly seared into our memories. Puzzlement at the first plane, shock at the second, and terror at the third and fourth. Throughout, there was a slowly emerging realization that this was no accident, that America was at war, and that our world had dramatically, irreversibly, changed.

That night, America went to sleep thinking that 10,000 people could be lying crushed in the burning rubble of New York City, Washington D.C., and Pennsylvania. When that number was eventually reduced to just under 3,000, the day felt no less evil. At the same time, we gave thanks for everyone that made it home and marveled at miraculous stories of survival and heroism. We feared that more attacks were inevitable.

Over the coming days and weeks, a new spirit was in the air. America found its moral clarity, national unity, and a deeper respect for the firemen, police officers, and first responders who had courageously run into the danger. We were more gracious to strangers and flew more American flags. In the days after 9/11, the lines between "us" and "them" were shifted, though not always in good ways. Even in Congress, at least for a short time, national divisions seemed far less important than our shared national identity.

There was something deeper to all of this than a shared experience of pain. In the end, for a time, our national conversations were reframed by a shared witness of evil. Destroyed with the Twin Towers were postmodern pretensions about the malleability of truth and ethics. Gone, for a time, was any talk of "your truth" vs. "my truth." We had witnessed it with our own eyes: Good was good and evil was not. There were heroes, and there were villains. There were New York's Finest rushing into the danger, and there were the vile assassins that brought destruction.

It was as if we'd been awakened from an ideologically-formed dreamworld to the real one. For a while, long-suppressed truths about the human condition and the reality of evil were undeniable, having breached the surface of our hearts, minds, and culture. Pain, wrote C.S. Lewis, is God's megaphone. And, for a moment, our collective pain allowed us to see more clearly than we had without it. Sadly, it was only for a moment.

In the months after 9/11, a well-known Christian apologist confidently announced that postmodernism was dead. After witnessing the evil of that day, no one, he suggested, would embrace a worldview that denied absolute truth or morality. He was wrong.

Eventually, a postmodern culture made sense of the day by retreating to its postmodernism. Rather than conclude that the evil of 9/11 required that moral absolutes must exist, the narrative became that the evil of 9/11 was because of those who embraced moral absolutes. Once the obvious contradiction is set aside, it's a short step to a different kind of absolutism, in which evil is called good and good is called evil. Of course, any of the collective spirit and national identity from those pain-filled days is long gone as well.

To be clear, reality is not gone. Our ability to see it is. God willing, we'll never see another day like 9/11. God willing, we'll find ways to recapture the awareness of what is true and good without another day like that.

The very least we can do is to remember, not just what happened that day and what it meant to us, and not even just the pain we felt. We must remember what the pain taught us. We must remember that categories of good and evil are far more than culturally conditioned preferences. We must remember that virtue consists of more than silly slogans of tolerance or plays for power.

We must remember how the trendy philosophies about reality and morality that were so popular on September 10 simply weren't big enough for September 11, that our ideas about God and truth and morality have consequences, and that our bad ideas have consequences. We must remember that God is real, truth is real, morality is real, and human dignity is worth fighting for.