Mark 9:28 Meaning

26And the spirit cried, and rent him sore, and came out of him: and he was as one dead; insomuch that many said, He is dead.

27But Jesus took him by the hand, and lifted him up; and he arose.

28And when he was come into the house, his disciples asked him privately, Why could not we cast him out?

29And he said unto them, This kind can come forth by nothing, but by prayer and fasting.

30And they departed thence, and passed through Galilee; and he would not that any man should know it.