A decorated American soldier has allegedly become a mass murderer. Why? How? Well, look inside your own heart.

“The line separating good and evil passes not through states, nor between classes, nor between political parties either, but right through every human heart.”

These words, penned in 1973 by then-Soviet dissident and Christian writer Aleksandr Solzhenitsyn, brilliantly sum up the human condition after the Fall.

And they explain the shocking tragedy of Staff Sargent Robert Bales, the U.S. soldier who allegedly murdered 16 Afghan civilians – women and children among them – in cold blood.

You know the story. Bales was on his fourth combat tour. He was a decorated soldier, a family man, well-liked and respected by his superiors and his neighbors. But on that fateful night, something inside Bales’s mind or soul went horribly wrong. He left his base for a nearby village, we are told, and went on a wild rampage of evil.

But how, why? Did he “snap” as we are hearing and reading about? Was the pressure of four combat tours too much? Did seeing his friend lose a leg the day before set him off? Was he indeed drinking that night?

Well, those could all be factors. But back to Solzhenitsyn: In describing the line separating evil and good in the human heart, he also had this to say: “This line shifts. Inside us, it oscillates with the years. Even within hearts overwhelmed by evil, one small bridgehead of good is retained; and even in the best of all hearts, there remains a small corner of evil.”

The tragedy in Afghanistan should remind us all that evil is real. That the biblical account of fallen human nature is true. David Brooks in the New York Times this week rightly cited G.K. Chesterton, who wrote that original sin “is the only part of Christian theology which can really be proved.”

And it is proven, over and over, throughout history. In my book Being the Body, I tell the story of Nazi mass murderer and Holocaust mastermind Adolf Eichmann. Kidnapped in 1960 by Israeli agents, he was put on trial in Israel.

One witness against him was an Auschwitz survivor named Yehiel Dinur. Dinur entered the courtroom and stared at Eichmann. Their eyes met. After a few tension-filled moments, Dinur broke down and began to shout and sob. Why? Was it the memories of Auschwitz? Was Eichmann evil incarnate?

No, as Dinur explained on 60 Minutes, it was the fact that Eichmann was an ordinary man. Dinur saw so clearly that sin and evil are part of the human condition. “I was afraid about myself. I saw that I am capable to do this … Eichmann is in all of us.”

Justice demands that Staff Sgt. Bales be tried for his crimes. But as we soberly, mournfully ponder what happened that night in Afghanistan, we must remember that we human beings, made in God’s image though we are, are nonetheless fallen. That although we are capable of the most sublime acts of charity, goodness and beauty, we are also capable of the most outrageous acts of depravity.

And only the Christian worldview gives us the ability to see things – even human nature – as they really are. And if we cannot understand things the way they are and live our lives accordingly, then God have mercy on us all.