Contradiction with Mark 9:24
While Matthew 17:15 illustrates the father's lack of faith in describing his son's condition, Mark 9:24 shows the father expressing belief and asking for help with his unbelief.
Mark 9:24: And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief.
Contradiction with John 9:3
Matthew 17:15 implies the boy's condition resulted from demonic possession, whereas John 9:3 suggests that such afflictions are not necessarily due to sin or possession, but for God's works to be revealed.
John 9:3: Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him.
Contradiction with James 5:14-15
Matthew 17:15 describes a case of demonic possession, whereas James 5:14-15 suggests different reasons for illness and their healing through prayer rather than exorcism.
James 5:14-15: Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord:
Contradiction with 2 Corinthians 12:7-9
Unlike Matthew 17:15, which implies a need for healing from possession, 2 Corinthians 12:7-9 depicts a “thorn in the flesh” accepted as God's will to keep the person humble.
2 Corinthians 12:7-9: And lest I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh, the messenger of Satan to buffet me, lest I should be exalted above measure.
Contradiction with Matthew 17:20
While Matthew 17:15 shows the disciples unable to heal due to lack of faith, Matthew 17:20 contradicts it by stating faith as small as a mustard seed can move mountains, suggesting even small faith should have been enough.
Matthew 17:20: And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
Contradiction with Matthew 4:24
Matthew 17:15 speaks of a specific instance of possession, while Matthew 4:24 generalizes that many brought to Jesus were possessed and healed without questions of faith.
Matthew 4:24: And his fame went throughout all Syria: and they brought unto him all sick people that were taken with divers diseases and torments, and those which were possessed with devils, and those which were lunatick, and those that had the palsy; and he healed them.
Paradox #1
The potential contradiction in that verse could be the attribution of a medical condition to supernatural causes. In modern science, medical conditions are typically explained by biological or neurological factors rather than supernatural influences.