Today's Gospel is the story of the boy possessed by a mute and deaf spirit whom Jesus meets as He comes down the mountain after the Transfiguration.
The story contains that wonderful prayer, "I do believe, help my unbelief!," and that great promise, "Everything is possible to one who has faith." We laugh at the blockheadedness of the disciples that drew from Jesus the rebuke, "O faithless generation, how long will I be with you? How long will I endure you?" (There's so much going on in this story that we may never get around to thinking about the rebukes our own blockheadedness draw from Him.)
In all this, the mute spirit possessing the boy comes off as something of a Macguffin. It's just there to get the plot rolling, an indifferent means to the end of revealing the many things God reveals in the passage.
It might repay the time, however, to take a closer look at this mute spirit. Here are two lines of thought:
First, courtesy of Fr. John Dear, SJ, in his book Transfiguration, note that the spirit "has often thrown him into fire and into water to kill him." In the New Testament, fire and water symbolize the Holy Spirit and baptism, sources of life. The spirit, though, tries to use them as the means of death*. Jesus' word overcomes these "anti-sacraments" (as I say, this is a line of thought; you'll have to do the shading yourself), since He has come to bring life to the dead.
Second, the father says that, when the spirit seizes his son, "he foams at the mouth, grinds his teeth, and becomes rigid." Do you know anyone in your own life who has a tendency -- perhaps when the subject turns to religion or politics or morality -- to foam at the mouth, grind his teeth, and become rigid? Perhaps, and this is offered without the implication that there is a demonic spirit at work, perhaps the way forward in truth with this person is only through prayer (and, as a variant, through fasting).
*:It's interesting to note that, for the Jews, water readily signified death. Gentle rain and peaceful streams were all to the good, but if you have too much water in one place you can drown. Witness the disciples' terror at the storms on the Sea of Galilee. As for sailing on the Mediterranean, that was best left to the pagans. When the Psalmist felt overcome by woe, he called to the LORD "out of the depths." Yet, time and again, Jesus told His disciples, "Be not afraid," even as He told them, "Put out into the deep."