When my family moved to Elgin, IL last July, we visited many congregations in search of a church home. At one small Episcopal church, the rector discovered I had come to Illinois in order to work with Christian History magazine. He was visibly excited. "That's just what the church needs!" he said.

I probed: Why was he so convinced Christians today need to know church history? The rector's response was memorable: "Because God's gift of teaching has a long shelf life."

In other words, even though the church has lived out the faith in many different cultures and faced many different challenges through its 20 centuries, God has given certain leaders words of wisdom that never seem to lose their relevance. (That's just the kind of God he is—the kind who entered history in the person of Jesus Christ, and has never left it.)

Ten days after September 11, 2001, we posted on this website a CH article by Robert L. Holmes, on Augustine's teachings about "just war."

With the conflict in Iraq now underway, many are asking whether, as Christians, we should condone this war. And the wise thoughts of Augustine—definitely one of those "long shelf life" teachers—are still available to us, though he died over 1500 years ago.

We thank Dr. Holmes for exercising his own teaching gifts to bring those ancient-but-relevant thoughts to us, and we turn to hear them again:

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The fall of Rome in 410 was a calamity of staggering proportions to the citizens of the Roman Empire. Civilization itself had been shaken to its foundations.

So it was viewed by Augustine, from his vantage point on the North African coast. But he worried not so much about the empire as about the threat of a backlash to Christianity.

Hadn't critics warned for years that Christians' pacifism would weaken the empire? Didn't this confirm the fears that Christianity was too other-worldly for its followers to be responsible citizens of the state?

Though church and state had worked together for nearly a century (since the conversion of Constantine), Augustine still felt that he needed to establish once and for all that Christians could in conscience assume the full obligations of citizenship, including participation in warfare.

The task was a challenge. Critics seemed to have on their side the teachings of Jesus himself. Though Jesus never talked about war directly, his message of love, humility, and compassion seemed incompatible with violence and killing. And so it was understood by most early Christians.

However, Augustine had already argued (in his attack on the Manichees) that, properly understood, Jesus' teachings did not in all cases call for literal obedience. Of Jesus' injunction, "If someone strikes you on the right cheek, turn to him the other also," Augustine said, "What is here required is not a bodily action, but an inward disposition. The sacred seat of virtue is the heart."

To illustrate this priority of inward motive, Augustine asked readers to consider a man hitting a boy and another man caressing a boy. The first case seems bad, but the man might be a father lovingly disciplining his son; the second case seems good, but the man might be a child molester. Thus, Augustine said, "We find a man by charity made fierce; and by iniquity made winningly gentle."

Because God judges the soul, the ultimate question is not "what the man does … but with what mind and will he does it." The appropriate motive in all cases, Augustine rules, is love. What is done from love of God must be good.

This opens the door for Christians to perform outward acts that might appear to be forbidden by Scripture. Still, there had to be a rationale for stepping through the door, and Augustine gave that rationale in City of God.

There Augustine insists there is no "private right" to kill. One can kill only under the authority of God, as communicated by direct or implicit command from God, or by a legitimate ruler who carries out God's intent to restrain evil on earth. Augustine further suggests that one who obeys such a command "does not himself 'kill.'" He acts only as an instrument of the one who commands.

Augustine concludes, "The commandment forbidding killing was not broken by those who have waged wars on the authority of God, or those who have imposed the death-penalty on criminals when representing the authority of the state, the justest and most reasonable source of power."

When there is no command by God, war may be waged only by those with legitimate authority, and only for a just cause. Augustine was not, however, specific on what causes can be considered just. He has been interpreted narrowly, as saying states may go to war to avert (defensively) or avenge (offensively) a violation of their rights, or broadly, as saying war may be waged to redress any wrong against God's moral order.

Thus Augustine fashioned what is now called the "just war theory," which over the centuries has become a complex set of criteria to govern both the recourse to war in the first place and the conduct of war once begun.

According to this justification, theologian Paul Ramsey contends in The Just War, Christian participation in warfare "was not actually an exception [to the commandment, "You shall not murder"] … but instead an expression of the Christian understanding of moral and political responsibility."

This understanding has, of course, been challenged from many angles. But with the exception of the "peace churches" (Quakers, Brethren, and Mennonites), mainstream Christianity has stayed to the present day essentially on the course set by Augustine.

Robert L. Holmes is professor of philosophy at the University of Rochester and author of On War and Morality (Princeton, 1989). This article originally appeared in Christian History issue 67: Augustine.