John Lightfoot on Matthew 17:17

[O faithless and perverse generation, &c.] The edge of these words is levelled especially against the scribes (see Mark 9:14); and yet the disciples escaped not altogether untouched.

Christ and his three prime disciples being absent, this child is brought to the rest to be healed: they cannot heal him, partly, because the devil was really in him; partly, because this evil had adhered to him from his very birth. Upon this the scribes insult and scoff at them and their master. A faithless and perverse generation, which is neither overcome by miracles, when they are done, and vilify, when they are not done! The faith of the disciples (v 20) wavered by the plain difficulty of the thing, which seemed impossible to be overcome, when so many evils were digested into one, deafness, dumbness, phrensy, and possession of the devil: and all these from the cradle.