Why could we not cast it out?

Matthew 17:14-20

“This is faith… it is as we surrender, as we both acknowledge the limits of our own power to bring about transformation, and trust our whole selves in God as conduits of love and makers of peace, knowing full well that joining in the suffering of the world will bring about our own suffering, but that it will also bring about our healing and salvation. That is the power of an active faith!”
— Todd Bratulich