IN EIGHT years as pope, Benedict XVI’s boldest act may have been his last one. His planned abdication at the end of this month, which took the world and most of the Catholic Church by surprise, would be the first by a pope in nearly 600 years. Though the Vatican said he was not suffering from any life-threatening ailment, the 85-year-old pontiff concluded that he lacked the “strength of mind and body” to carry out his ministry in a world “subject to so many rapid changes and shaken by questions of deep relevance for the life of faith.”

The hallmark of Pope Benedict’s tenure, for better or for worse, was fierce resistance to those changes. He rejected calls by Catholic progressives for reconsideration of doctrines such as celibacy and the ban on women in the priesthood; at a time when acceptance of the rights of gays and lesbians is rapidly spreading across the world, he was outspoken in condemning homosexuality as “unnatural” and unacceptable. With sectarian tension growing in Europe as well as the Middle East, he eschewed dialogue with Muslims and infuriated many by quoting a condemnation of Islamic theology as “evil and inhuman.”

The pope presided over a faith whose demographic center of gravity has shifted to Latin America, Africa and Asia, yet he chose to focus his ministry on an attempt to revive Catholicism in Europe, including its most conservative elements. By some important measures, he failed. Church membership continued to decline even in Germany, his native country and the site of his best-received tour. In the developing world, once-growing Catholic churches lost ground to other faiths.

Pope Benedict’s response to the greatest challenge he faced — the explosion of sexual-abuse scandals in Catholic dioceses around the world — was inadequate. During his visit to the United States in 2008, he met with victims of predatory priests; he later apologized for the crimes and oversaw modest Vatican measures to extend the statute of limitation for cases and prevent further abuse. But the pope never acted against bishops who covered up crimes, and he never admitted or apologized for his own failures during the years when, as Cardinal Joseph Ratzinger, he headed up the Vatican body charged with disciplining priests.

Some of Pope Benedict’s most important achievements came in response to the backlash triggered by his reactionary acts. Pilloried for having suggested before a tour of AIDS-stricken Africa that the use of condoms “increases the problem,” he later suggested that the use of a condom by an HIV-infected person to avoid infecting a partner could be a positive step. After angering Jews by rehabilitating a bishop known as a Holocaust denier, the pope prayed at Auschwitz and published a book exonerating the Jewish people for the death of Jesus.

Pope Benedict will leave behind a church facing the same debilitating problems that loomed after the death of Pope John Paul II — above all, how to remain relevant to an increasingly secular world and to its own changing membership. This pope’s response was to insist that only uncompromising adherence to past doctrine could preserve the faith. Catholics who seek a different answer will have to hope that a college of cardinals dominated by the pope’s appointees will choose a more progressive successor.