By Dan Merica and Daniel Burke, CNN

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(CNN)– For more than two decades, the Rev. R. Guy Erwin couldn't officially be a pastor in the Evangelical Lutheran Church in America. On Friday, he was elected a bishop.

Erwin's election signals a shift not only for the ELCA – the nation's seventh largest church – but also for American Christianity. Only one other mainline Protestant denomination, the Episcopal Church, has elected openly gay and lesbian bishops.

“In these days such milestones seem to be coming at an ever-faster rate," Erwin told CNN, "and eventually what seems revolutionary now will seem normal and predictable."

With more than 4 million members in 10,000 congregations, the ELCA is the largest of several Lutheran denominations in the United States. The ELCA's decision to allow gay clergy has strained ties between those denominations, some of whom have partnered for relief work.

"The ELCA is a church that belongs to Christ, and there is a place for all here," said church spokeswoman Melissa Ramirez Cooper. "The election of Pastor Erwin illustrates what many in the 4-million-member church believe - that God calls each of us by name.”

The ELCA lifted its ban on openly gay, partnered clergy in 2009, clearing the way for pastors like Erwin, but angering conservatives. By some estimates, some 600 congregations have since left the ELCA for more conservative churches.

The Rev. W. Stevens Shipman, director of the Lutheran Coalition for Renewal, said the ELCA is not keeping promises it made in 2009 to respect the views of churches and individuals who regard homosexuality as a sin.

"The promise was also made publicly that no congregation would be required to call a pastor in a same-sex partnership," Shipman said, "but now an entire synod has been forced to live under the authority of a bishop who is in such a relationship."

Erwin, a scholar at California Lutheran University, will serve a six-year term representing the Southwest California Synod, a five-county area that includes Los Angeles. His election took place an annual three-day assembly in Woodland Hills, California.

Erwin, who was ordained a pastor in 2011, played down his election as the ELCA's first openly gay bishop. But acknowledged that his very “existence” was a symbol for broader acceptance.

“The work of a bishop in our church is to lift up the church's message of grace and peace in the wider society, to administer the church's work in our area, and to teach and preach,” Erwin said in an e-mail to CNN. “In this regard, the sexual orientation of the bishop may not be very important.”

Still, the bishop-elect said, “The very fact I exist will be a signal to others that GLBT folks are respected and have a full place in our church.” Erwin is also part Osage Indian and is active in the Osage Indian Nation, according to the ELCA.

Erwin’s election symbolizes a noticeable change for a church that once banned clergy who were in same-sex relationships, said Ross Murray, director of news and Faith initiatives at GLAAD.

Prior to the 2009 change, “hundreds of gay and lesbian clergy were forced out of congregations or served under secrecy,” Murray said.

“Dr. Erwin demonstrates how far the ECLA has come with LGBT inclusion,” said Murray in an e-mail to CNN. “He could not have been ordained just four years ago, and now he is a leader for the church. It makes me proud as a gay man, and as a Lutheran.”

Although the ELCA church did not allow clergy in same-sex relationships while he was attending seminary, Erwin said that he “always believed that this would someday be possible.”

Erwin also said the church's 2009 change in policy was more of a "culmination of God's work" than a "start of something new."

Erwin has long been a board member of Extraordinary Lutheran Ministries, a Lutheran group that advocates for the 130 openly gay Lutheran clergy who are members.

Amalia Vagts, the group’s executive director, said Erwin’s election was an “amazing day” for openly gay and lesbian Lutherans.

“This is a powerful message for LGBT people everywhere that the Lutheran church welcomes them,” Vagts said in an e-mail.