Gibbon Chapter XLVII: Christianity in the East
This chapter is a masterful summary of the theological discussions of the origin of the Incarnation and also of the later development - up to Gibbon's own day - of the history of the Nestorians, Jacobites (Syrian rather than Scottish), Maronites, Armenians, Copts, and Abyssinians. See also my notes on Ethiopia, king Alfred, and Cosmas Indicopleustes.