Missionary failure stemmed from missing language training and disputation skill.

Evidence

Llull acknowledges that there are indeed many devout clerics who do go off and preach to infidels: yet, since they lack specialized education in disputation, they are ineffectual. Moreover, not knowing the language, they resort to unreliable interpreters, and hence receive only the scorn of more educated infidels. — John V. Tolan, Saracens, 1330

Categorization

• SEED: Angle: early arguments for professionalized cross-cultural communication — the same ‘interpreter problem’ recurs today in diplomacy, journalism, and missionary work.