"When you were younger," Our Lord said to Peter, evoking with deep insight how life seems to a carefree boy, "you used to dress yourself and go where you wanted; but when you grow old, you will stretch out your hands, and someone else will dress you and lead you where you do not want to go."

The Gospel writer adds, "He said this signifying by what kind of death he would glorify God," in reference to the phrase, "you will stretch out your hands," because St. Peter was crucified, upside down, by Nero on Vatican hill. However, the rest of the remark, "someone will lead you where you do not want to go" applies to all of us.

We are reminded that, as St. Thomas Aquinas says, the Gospel is a law, the "New Law" as opposed to the "Old Law." As a law, it must share in the essence of any law, which is that it is a precept of reason which promotes the common good. St. Thomas explains that, as the word "law" (Latin, "lex") comes from the word "ligare," "to bind," any law must essentially bind those subject to it, "in the manner of rule and a measure." Peter as a mature Christian, and no longer a carefree boy, was now bound by the law of the Gospel.

We feel the binding force of a law when it goes against our proclivities, especially when it appears as a sudden, uninvited cross -- an accident, an unexpected diagnosis, an unanticipated crime.

But what is this "Law"? We gain insight from the reflections of Pope Benedict during his pilgrimage last week to the Fosse Ardeatine, the "Ardeatine Pits," located just outside of Rome, the scene of a horrific mass murder during the Nazi occupation of Rome.

The worst crimes, although always arising from twisted human will, seem to have the most capricious origins -- a combination of bungling, mistake, incompetence, and folly -- completely incommensurate with what the crime implies for the victims. This rule applies to an everyday abortion as much as to the murders of Capote's "In Cold Blood," and similarly as regards the massacre of the Fosse Ardeatine. On March 23, 1944, just a few weeks before Rome was liberated, a band of "partisans," largely communist resistance fighters, detonated a bomb in the midst of a parade of a German police force, killing 33 policemen. The policemen were actually Italians from the north who had joined the police precisely to avoid serving in the German army. The partisans eluded capture. The Nazi officials in Rome consulted Hitler about a reprisal, who ordered that 10 Italians were to be killed for each policeman, and that the executions be completed within 24 hours.

After putting together every remaining Jew in prison (about 70 of them), and others already in custody, guilty or not, the Nazis were still short of victims and rounded up civilians at random. But in their haste they took 335 instead of 330.

By their subsequent actions the Nazis signaled that they knew their deeds were evil. They killed the Italians in secret, bringing them to deserted "pits" in a desolate spot. They shot the prisoners in groups of five deep inside the caves. To finish the grisly task, the Nazis had to make themselves drunk with cognac, provided by high command. A demolitions unit blew up the entrance of the cave in hopes of sealing the entrance permanently.

And yet despite the Nazi attempts to dehumanize the victims and hide their crimes, after the war the victims were exhumed and properly buried, and on March 24, the anniversary of the murders, Popes and saints and civic leaders make a pilgrimage to the Fosse Ardeatine to honor its martyrs before the world.

St. Thomas says that the first and dominant note of the New Law is that it is grace, a gift. Pope Benedict in his address drew attention to a prayer scrawled on a piece of paper found in the pocket of one of the victims: "God my great Father, we pray to you that you might protect the Jews from the barbaric persecutions. 1 Pater noster, 10 Ave Maria, 1 Gloria Patri." Amidst the carnage and murder -- grace: concern for others, and the gift of brotherly love.

But then, St. Thomas says, the New Law commands external acts, "some which are necessarily in keeping with inward grace consisting in faith that worketh through love. Such external works are prescribed in the New Law; thus confession of faith is prescribed, and denial of faith is forbidden."

In his reflections, Pope Benedict drew attention to such a confession, scratched on a wall of a Nazi prison in Rome: "I believe in God and in Italy / I believe in the resurrection / of the martyrs and heroes / I believe in the rebirth / of the fatherland and in / the freedom of the people." The pope praised the purity of its sentiments, adding that: "Every man is called to realize his dignity in this way: witnessing to that truth that he recognizes with his conscience."

These witnesses or "martyrs" of the Fosse Ardeatine testify to us in Lent about the gift that we all share, of the Cross and of conformity to Christ: "A new commandment I give you" -- a New Law -- "love one another, in the very way that I have loved you."

Michael Pakaluk is Professor of Philosophy at Ave Maria University. His latest book about his late wife, Ruth, has just been published by Ignatius Press under the title, "The Appalling Strangeness of the Mercy of God."