Matthew 17:15

“Lord, have mercy on my son, for he is epileptic, and suffers grievously, for regularly he falls into the fire, and regularly into the water.”

He asked Him to have compassion of his son. Here the son is described as ‘affected by the moon' (lunatic), translated as epileptic because of the symptoms, and also, some have suggested, because epileptics were seen as ‘moonstruck'. But in Mark it is made clear that he is possessed by a ‘dumb spirit', and that this was thus no ordinary epilepsy. It is unlikely that the Apostles would have been thwarted by an ordinary case of epilepsy. The presence of this evil spirit is confirmed here by the fact that it is stressed that it tends to cause the son to be cast into either fire or water. The suggestion appears to be that it happened to an abnormal extent, as though the demon had perverse pleasure in being selective, although it may simply be that the father vividly remembered such incidents and was using them to impress on Jesus the seriousness of the situation.

‘Lord.' This was probably showing due reverence to a recognised prophet.