"God delights in faith. Jesus seems staggered at the disciples’ unbelief when he asks, ‘How is it that you have no faith?’ (Mark 4:40). In Mark 6:6 it says, ‘He was amazed at their unbelief’ (my italics). In Mark 9:19 he said, ‘O unbelieving generation, how long shall I stay with you? How long shall I put up with you?’ Was Jesus having a bad day? Was he demonstrating some true humanity by getting fed up? No! Jesus was innocent and perfect, the exact representation of God. He was wholly consistent with his Father who complained in Numbers 14:27, ‘How long shall I bear with this evil congregation …?’ and ‘How long will this people spurn Me? How long will they not believe Me?’ (Num. 14:11 NASB).
Jesus was weary of his unbelieving followers. He could not be indifferent or complacent. He could not passively accommodate their failure. As J I Packer says, ‘Moral indifference would be an imperfection in God.’ When Jesus rebuked their unbelief it was a revelation of his heart. He was not like an indulgent uncle or grandfather. He expected better from them! He wanted better from them! He found their unbelief unacceptable! His anger was pure, holy and appropriate! If their unbelief was not worthy of his reproach, Jesus would not have given it.Jesus served his Father with red hot zeal and holy passion. He looked for the same in his disciples. When, in Mark 9:28, the disciples asked, ‘Why couldn’t we drive it out?’ Jesus replied, ‘This kind can come out only by prayer’ (Mark. 9:29). Notice that he didn’t say, ‘This kind only comes out if it is God’s will.’ He said that they only come out if you pray.
If you pray it will happen. If you don’t it won’t!"