A former general secretary of the Reformed Church in America, Granberg-Michaelson is the author of "Future Faith: Ten Challenges Reshaping Christianity in the 21st Century." In the book, he examines major influences on the faith and practice of Christianity in the world today and what they mean for the church in America.

The first step for Christians in the United States, Granberg-Michaelson said, is to recognize that they are part of a vibrant global faith.

"It would help American Christians if they reframed their own narrative to see that they're part of a faith that is thriving globally," he said. "It's complicated, but it's actually pretty exciting."

To do that, U.S. Christians must recognize "a few simple things."

"One is that we have to de-Americanize the gospel," he said. "We have to grasp the gospel in its real intent instead of interpreting it through this shroud of nationalism, which sometimes gets really extreme and causes all kinds of problems."

That means that Christians in the U.S. can no longer read the Bible simply through the lens of American culture.

"We need to open ourselves to the voices and the movements of Christianity outside our own culture, and that will open up the deep reality of the gospel to us," he said.