And when they had come to the multitude, a man came to Him, kneeling down to Him and saying, 15 “Lord, have mercy on my son, for he is an epileptic and suffers severely; for he often falls into the fire and often into the water. 16 So I brought him to Your disciples, but they could not cure him.”
17 Then Jesus answered and said, “O faithless and perverse generation, how long shall I be with you? How long shall I bear with you? Bring him here to Me.” 18 And Jesus rebuked the demon, and it came out of him; and the child was cured from that very hour.
19 Then the disciples came to Jesus privately and said, “Why could we not cast it out?”
20 So Jesus said to them, “Because of your unbelief; for assuredly, I say to you, if you have faith as a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you. 21 However, this kind does not go out except by prayer and fasting.” — Matthew 17:14-21.
“Lord, have mercy on my son” (v.15). The title “Lord” (kurios) can simply mean “sir” or “mister” (lit. kurie). Here he is imploring Jesus as One having the power or authority to cure.
Will Jesus have mercy as the man requested? This is the question which the OT had predicted, the Messiah would have mercy (cf. Isa. 35:2-6; 61:1-2). Jesus’ power and compassion (cf. Matt. 9:27; 15:22; Mark 10:47,48; Luke 17:13) were the “signs” that the Jewish leadership sought!
A detailed account of this ailment is found in Mark 9:18-20. The term “epilepsy” was literally the term “lunatic” (Greek: “he acts lunatic”). This particular illness was caused by a demon (cf. Matt. 17:18). There is a major attempt in the New Testament to differentiate between demon possession, which often causes physical ailments, and physical disease itself (cf. Matt. 4:24). This was an account of an exorcism, not a healing.
“I brought him to Your disciples, but they could not cure him” (v.16). This was highly unusual, for Matt. 10:1,8 tells us they had this delegated power. The exact reason for their failure in this instance was specified as their lack of faith and prayer. A much more detailed account of the dialogue between the father and Jesus is recorded in Mark 9:21-24.
“And Jesus answered and said, ‘You unbelieving and perverse generation'” (v.17). This was an allusion to Deut. 32:5,20. In Jesus’ temptation experience (i.e., Matthew; Luke 4), He quoted Deuteronomy three times. He must have known and loved this book.
Jesus rebuked the demon, and it came out of him; and the child was cured from that very hour (v.18). A more graphic account is found in Mark 9:26. It must be remembered that each of the Gospel writers recorded these accounts in his own way for his own unique purposes and audiences. Therefore, it is important to try to understand each of them individually before consulting the others and combining the information (cf. Gordon Fee and Douglas Stuart in How to Read the Bible For All Its Worth, pp. 113-134).
“Why could we not cast it out?” (v.19). The disciples come to Jesus privately and ask Him why they failed. Jesus answers this question in Matt. 17:20 where He said, “Because of your unbelief.” “You have so little faith.” This was a repeated comment by Jesus (cf. Matt. 6:30; 8:26; 14:31; 16:8).
Then He tells them that if they had faith as small as a mustard seed, they would be able to accomplish great things and nothing would be impossible for them. The mustard seed was the smallest seed known to the Jewish people. Jesus was not emphasizing the power of human faith itself, but the object of their faith. Jesus was not disparaging their need for faith; it is crucial (cf. Heb. 11:1). From Matt. 21:21 it seems that “little faith” is characterized by Jesus as “doubt.”
“However, this kind does not go out except by prayer and fasting.” This account implies that there are different kinds of demons which require different techniques to deal with. Much faith, prayer, and self-denial (fasting) were necessary to eject the current type of demon.