At the start of the 13th century, in a crumbling wayside chapel in central Italy, a penitent spendthrift was praying before an ancient crucifix when he heard a voice speak to him: "Go, Francis, and repair my house, which as you see is falling into ruin."

The young man took the divine command to heart, and in one of the most enduring conversion stories of Christianity, Francesco Bernadone - later known as St. Francis of Assisi - renounced his worldly belongings and devoted himself to a life of poverty and service. He gathered around him a group of like-minded mendicants, and founded a religious order that would help reform a medieval church plagued by corruption in Rome, sexual sins among the clergy, and social upheaval among the laity.

Some 800 years later, one of his spiritual descendents, a Franciscan friar named Sean Patrick O'Malley, invoked the same phrase as he accepted one of the most daunting jobs in the Catholic universe - head of the Archdiocese of Boston - amid what is widely viewed as the greatest church crisis of modern times. "I ask you, and plead with you: Repair my church," O'Malley said, dressed in his trademark brown robe and sandals.

As the epicenter of the clergy sexual abuse scandal, Boston is both a bastion of American Catholicism and, conversely, its weakest link. As Boston goes, many believe, so goes the rest of the 65-million-strong U.S. church. That makes the choice of O'Malley, who will be installed at a solemn Mass on July 30, perhaps the most crucial appointment of John Paul II's lengthy pontificate. And it raises a question: Can a humble friar once again rescue the Catholic Church?

If the answer is yes, it may be due to the important but often overlooked differences between clergy. O'Malley is a member of a religious order; his predecessor in Boston, Cardinal Bernard Law, is a diocesan clergyman, taught to thrive in the competitive matrix of chancery culture.

The divergence between the religious and diocesan ranks of priests begins at the moment of ordination. Priests ordained to religious orders - such as the Franciscans, Dominicans, Jesuits, Carmelites and the like - take vows of poverty, chastity and obedience, while priests ordained to a geographical diocese make promises - not vows -- to remain celibate and to be obedient to their local bishop. Of course, implicit in those promises for diocesan, or "secular" clergy as they are known, is the expectation that they will live a simple, Christ-like life. And the vast majority do.

But it is also possible for diocesan priests to own a home, or to salt away investments or an inheritance for retirement. Father Andrew Greeley, for example, is a Chicago priest and best-selling author who has made millions off his popular novels. But he has liberally dispensed his earnings, donating close to $2.5 million to the archdiocese and to the University of Chicago, where he teaches. Order priests generally do not have that option, and surrender anything they inherit or earn to their community of monks or friars.

Besides this egalitarian orientation, religious order clergy also tend to dedicate their lives to the poor, the sick, and the marginalized, often in missionary postings overseas. By contrast, diocesan clergy are likely to staff parishes and keep the machinery of the diocesan running. O'Malley, for example, first became a bishop in the U.S. Virgin Islands, where he promptly moved out of the previous bishop's grand residence and focused on ministering to the poor. Early in his career as a priest in Washington, D.C., he moved into vermin-infested housing in a run-down neighborhood. That kind of solidarity with the downtrodden is a hallmark of many religious orders, and particularly of Franciscan life. While Cardinal Law was feared as the basso profondo voice of Catholic orthodoxy, O'Malley embodies St. Francis' famous motto, "Preach the Gospel at all times. If necessary, use words."

That statement (while likely apocryphal) neatly sums up the Franciscan spirit and helps explain O'Malley's compassionate approach to victims of clergy sexual abuse, which differs markedly from that of many of his fellow bishops. That became evident a decade ago when O'Malley was named to head the diocese of Fall River, Mass., then the focus of a previous round of sex scandals. O'Malley earned a reputation for listening patiently to abuse victims, often for hours, and for negotiating out-of-court settlements that even had plaintiffs' lawyers praising him.

Thus it was no surprise when he was sent to the Diocese of Palm Beach last year after its second bishop in a row resigned in a sex scandal. This time around, with Boston in dire straits, Rome is desperate for a savior for the American church-and its choice of O'Malley makes perfect sense. Still, it has surprised veteran Vatican hands-and O'Malley himself, who hoped for a missionary assignment in Latin America - in part because he was installed in Florida just a few months ago.