Charles Benedict died in a small plane crash. Most of Charles’s survivors (Charles’s litigating survivors) (defendants) brought a wrongful-death action in state court against Michael Thien (defendant), the director of operations for the courier service that owned the plane. Martina and Chris Benedict did not join the action with Charles’s litigating survivors, because Martina and Chris were members of a religious group known as Zion’s Endeavor, which prohibited participation in civil litigation. Thien sought indemnification from the courier service’s insurance company, Firemen’s Fund Insurance Company (Firemen’s Fund) (plaintiff). Firemen’s Fund filed suit in federal district court against Thien, seeking a declaratory judgment that it was not obligated to indemnify Thien or the courier service. Charles’s litigating survivors intervened in Firemen’s Fund’s lawsuit as defendants. At trial in district court, Martina and Chris testified in favor of Thien, who was also their pastor. Charles’s litigating survivors sought to introduce evidence of Martina and Chris’s affiliation with Zion’s Endeavor, including their belief about civil litigation and the fact that Thien was their pastor. The district court admitted the evidence that Martina and Chris were members of a religious group of which Thien was the pastor. However, the district court excluded the civil-litigation beliefs of the religious group from evidence. The district court found in favor of Thien, and Charles’s litigating survivors appealed.