At the beginning of an evening worship service at the First Assembly of God Church in Steele, MO, the Rev. Ryan Harris pitted teens against adults in a trivia game called Battle of the Generations.

“The gift of the Holy Spirit is placed upon you, it’s placed inside you,” Harris told his congregation, his voice thundering through his headset to the back walls of the tiny church. “The Holy Spirit gives you strength to stand up to those who don’t want you to stay in school, who want you to try drugs, to try sex.”

It’s the Holy Spirit that provides Pentecostals with the practice that sets their movement apart from all other evangelical Christian churches: speaking in tongues, or glossolalia.

“The distinguishing feature of classical Pentecostalism is to say that unless you have spoken in tongues, you don’t have this baptism in spirit,” said Russell Spittler, emeritus professor of New Testament at Fuller Theological Seminary in California.

But during an hour of worship at First Assembly, no one audibly spoke in tongues, and elders in the Assemblies of God are worried about what a younger generation’s more practical theology might mean for the future of the practice.