The nine disciples were yet pondering upon the bitter fact of their own failure; and when Jesus was once more alone with them, they questioned, "Why could not we cast him out?" Jesus answered them, 430 "Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. Howbeit this kind goeth not out but by prayer and fasting." Their unbelief, that shut them out from deeper sympathy with 431 Christ, and the carelessness with which they regarded the sacred work committed to them, had caused their failure in the conflict with the powers of darkness.

De ni disciple undrede sig stadig over, at deres eget forsøg var mislykkedes, og da Jesus atter var blevet ene med dem, spurgte de: "Hvorfor kunne vi ikke uddrive den?" Jesus svarede dem: "Fordi I har så lidt tro; thi sandelig siger jeg eder: hvis I har tro som et sennepsfrø, kan I "sige til dette bjerg: Flyt dig herfra og derhen, så skal det flytte sig; og intet vil være umuligt for jer. (Den slags farer kun ud ved bøn og faste.)" Deres vantro havde lukket dem ude fra en dybere forståelse af Kristus, og den letsindighed, hvormed de betragtede den hellige opgave, der var blevet betroet til dem, havde været årsag til deres mislykkede bestræbelser i striden mod mørkets magter.