Mat 17:21 But this kind goes not out except by prayer and fasting.

There is a hidden meaning here. Christ seems to be referring to the "devil" of insanity that he caste out of the woman's son. However, Christ has never said anything about that devil in this entire dialogue. He has talked about only one thing: the doubt and disbelief of his generation and his followers. This is what Christ is really saying is eliminated by prayer and fasting.

"Kind" is from genos, which means "race," "offspring," "class," "sort," and "kind,"

"Goes out" is from ekporeuômai, which means "to make to go out" and "fetch out."

"Prayer" is from proseuchê, which means only "prayer." The verb form, proseuchomai, is usually used by Christ in his teachings. This is the first time that the noun is used.

"Fasting" is from nêsteia, which means only "to fast."