Mark 9:28

28 Jesus went indoors. Then his disciples asked him in private, "Why couldn't we drive out the evil spirit?"

Mark 9:28 Meaning and Commentary

Mark 9:28

And when he was come into the house
Perhaps into the man's house whose child he had healed, or into some other in these parts, for the sake both of retirement and refreshment:

his disciples asked him privately, why could not we cast him out?
The nine disciples, who were particularly concerned in this matter, fearing they had lost the power of casting out devils, conferred upon them, inquired of Jesus, when he was alone, why they could not cast the demon out of the child, when they had ejected unclean spirits out of many others; (See Gill on Matthew 17:19).

Mark 9:28 In-Context

26 The spirit screamed. It shook the boy wildly. Then it came out of him. The boy looked so lifeless that many people said, "He's dead."

27 But Jesus took him by the hand. He lifted the boy to his feet, and the boy stood up.

28 Jesus went indoors. Then his disciples asked him in private, "Why couldn't we drive out the evil spirit?"

29 He replied, "This kind can come out only by prayer."

30 They left that place and passed through Galilee. Jesus did not want anyone to know where they were.