Congregation Jeshuat Israel v. Congregation Shearith Israel

Issues: (1) Whether, in ordinary trust and property disputes, the establishment clause precludes courts from considering secular evidence that is relevant and admissible under governing state law merely because the litigants are religious parties; (2) whether, in ordinary trust and property disputes, excluding secular evidence that is relevant and admissible under state law merely because the litigants are religious parties violates the free exercise clause by treating religious parties differently from—and, here, less favorably than—secular parties; and (3) whether, in ordinary trust and property disputes, federal courts sitting in diversity may disregard governing state substantive law and fashion federal common law merely because the litigants are religious parties.