Mark 9:28

28 After the return of Jesus to the house His disciples asked Him privately, "How is it that we could not expel the 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 So with a loud cry he threw the boy into fit after fit, and came out. The boy looked as if he were dead, so that most of them said he was dead;

27 but Jesus took his hand and raised him up, and he stood on his feet.

28 After the return of Jesus to the house His disciples asked Him privately, "How is it that we could not expel the spirit?"

29 "An evil spirit of this kind," He answered, "can only be driven out by prayer."

30 Departing thence they passed through Galilee, and He was unwilling that any one should know it;