As a scholar, he’s charted the decline in religion. Now the church he pastors is closing its doors

They plan to gather one last time on Sunday — the handful of mostly elderly members of First Baptist Church in Mt. Vernon, Illinois.

They’ll say the Lord’s Prayer, recite the Apostle’s Creed and hear a biblical passage typically used at funerals, “To everything there is a season … a time to be born, and a time to die.” They’ll sing classic hymns — “Amazing Grace,” “It Is Well With My Soul” and, poignantly, “God Be With You Till We Meet Again.”

Afterward, members are scheduled to vote to close the church...