CHICAGO (AP) — Blase Cupich became the archbishop of Chicago on Tuesday after his predecessor handed him a bishop's staff and relinquished the chair that symbolizes the leadership of the nation's third-largest diocese.

During a Mass at Holy Name Cathedral, the transfer of power was completed as Cardinal Francis George, who is battling cancer, stepped aside to retire after being the spiritual leader of more than 2 million Catholics since 1997.

The installation of Cupich — who was bishop of the Diocese of Spokane, Washington, when he was selected by Pope Francis to succeed George — marks the first time in the history of the Chicago archdiocese that a new archbishop assumes leadership while his predecessor is still alive.

It also represents the pope's first major American appointment, and sends a message by replacing a leading conservative cardinal with the more moderate Cupich that the pope wants more focus on mercy and compassion instead of divisive social issues.

Cupich, 65, spoke forcefully Tuesday on the sexual abuse scandal that has plagued the church, including Chicago's archdiocese. In one of his last official acts, George released files on three dozen priests who had been accused of sexual abuse in the last 60 years and whose crimes were in many cases concealed by the archdiocese.

"Working together to protect children, to bring healing to victim survivors and to rebuild the trust that has been shattered in our communities by our mishandling is our sacred duty," he said, "as is holding each other accountable, for that is what we pledge to do."

As he comes to an archdiocese that has shrunk in recent years and been forced to close schools amid declining enrollment, Cupich also spoke of the "formidable task" of passing on the faith to the next generation and his desire to bring young people back to the faith.

Cupich voiced his support Tuesday for Pope Francis' call for leaders in the church to be pastors. He also emphasized mercy and reaching out to people instead of just simply lecturing them, to openly communicate with those with whom the church might disagree.

"Jesus invites us, not only to take the risk of leaving our comfort zone, but also to deal with the tension involved in change, not dismissively but in a creative way," he said. "Pope Francis is giving voice to this invitation in our day ... to leave behind the comfort of going the familiar way."

Cupich set the transition in motion Monday night. In a ceremony steeped in tradition and symbolism, he arrived at the cathedral — crowded with hundreds of priests, religious leaders from several faiths and civic leaders — and knocked on the door three times.

Those knocks, symbolizing his request to be admitted into the cathedral, started a process that included a presentation of a garment called an archdiocesan stole that represents an invitation by the priests in the archdiocese to be the pastor.

In his homily Monday night during what is called a Rite of Reception, Cupich said he intends to tone down the rhetoric that has driven young people away from religion. He also vowed to take an active role in the community, pushing for immigration reform, taking part in the battle against gangs and gun violence, among other issues.

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Associated Press writer Sophia Tareen contributed to this report.