One of America's largest Pentecostal denominations may be losing one of its defining characteristics—even as it continues to grow and diversify at an enviable rate.

As Assemblies of God (AG) leaders meet this week in Orlando for their biennial conference, recently released statistics paint a healthy portrait.

The AG's U.S. division grew more than twice as fast as the American population in 2012 (1.8 percent vs. 0.7 percent), gaining almost 54,000 adherents to now number nearly 3.1 million worshipers at more than 12,700 churches (up 127 from 2011). (Worldwide, the AG gained nearly 1 million adherents in 2012 to surpass 66 million.)

It is also increasingly diverse: Today, only 59% of U.S. adherents are white.

Such growth makes the AG increasingly distinct from other major Americans denominations—including the Episcopal Church, Evangelical Lutheran Church in America, Presbyterian Church (U.S.A.), and United Methodist Church—that continue to face steady ...

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