Most translations make a note in the margin that only some manuscripts of the New Testament include “fasting,” but as biblical scholar, Alan Cole notes, “There is some good… evidence for the addition of prayer and fasting at this point.” The fact of the matter is this passage is all about dependence on God, and there is nothing like fasting to call our attention to our need for God. Jesus is calling the disciples to a place of greater spiritual dependence.
During these 21 days, one of the best things that will happen is that you will become more and more aware of how much you need God. No matter who you are, you cannot do what God has called and created you to do without His help!
Mark 9:14-29 ESV
And when they came to the disciples, they saw a great crowd around them, and scribes arguing with them. And immediately all the crowd, when they saw him, were greatly amazed and ran up to him and greeted him. And he asked them, “What are you arguing about with them?” And someone from the crowd answered him, “Teacher, I brought my son to you, for he has a spirit that makes him mute. And whenever it seizes him, it throws him down, and he foams and grinds his teeth and becomes rigid. So I asked your disciples to cast it out, and they were not able.” And he answered them, “O faithless generation, how long am I to be with you? How long am I to bear with you? Bring him to me.” And they brought the boy to him. And when the spirit saw him, immediately it convulsed the boy, and he fell on the ground and rolled about, foaming at the mouth. And Jesus asked his father, “How long has this been happening to him?” And he said, “From childhood. And it has often cast him into fire and into water, to destroy him. But if you can do anything, have compassion on us and help us.” And Jesus said to him, “‘If you can’! All things are possible for one who believes.” Immediately the father of the child cried out and said, “I believe; help my unbelief!” And when Jesus saw that a crowd came running together, he rebuked the unclean spirit, saying to it, “You mute and deaf spirit, I command you, come out of him and never enter him again.” And after crying out and convulsing him terribly, it came out, and the boy was like a corpse, so that most of them said, “He is dead.” But Jesus took him by the hand and lifted him up, and he arose. And when he had entered the house, his disciples asked him privately, “Why could we not cast it out?” And he said to them, “This kind cannot be driven out by anything but prayer.”
John 15:4-5 ESV
Abide in me, and I in you. As the branch cannot bear fruit by itself, unless it abides in the vine, neither can you, unless you abide in me. I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing.