While angels are “ministering spirits sent to serve, for the sake of those who are to inherit salvation” (Heb 1:14), devils are humans’ enemies, “prowling around like a roaring lion looking for [someone] to devour” (1 Pt 5:8). The harm of the demon is shown in the possessed person: He suffers severely; often he falls into fire, and often into the water.

Angels love human beings, guard them, and represent them before God’s throne, while devils hate humans, are jealous of them, and seek the destruction of their body and soul. Devils are spirits and so are powerful. Even if the disciples are given the authority by Jesus to cast out demons, in one instance in the Gospel, they are not able to cure the possessed man.

Jesus points to their “little faith” (vv 17, 20). Maybe they rely more, or even take pride, on their own capacity, rather than put their trust in the Lord. If faith is absent, even using the name of Jesus as a kind of magical prayer will not do, as the Jewish exorcists, the seven sons of Sceva found out in Ephesus. The person with the evil spirit sprang at them and subdued them all (Acts 19:14-16). There are people, even among Church people, who diminish the power of Jesus over the devil, saying that he cured people with mental illness, not as possessed by evil spirits.

While it is true that people in early times could confuse epilepsy with demonic possession, it is also true that there was the devil. The devil would take delight in having us mistake or trivialize his presence.

Moses said to the people: “Hear, O Israel! The Lord is our God, the Lord alone! Therefore, you shall love the Lord, your God, with all your heart, and with all your soul, and with all your strength. Take to heart these words which I enjoin on you today. Drill them into your children. Speak of them at home and abroad, whether you are busy or at rest. Bind them at your wrist as a sign and let them be as a pendant on your forehead. Write them on the doorposts of your houses and on your gates.

“When the Lord, your God, brings you into the land which he swore to your fathers: Abraham, Isaac, and Jacob, that he would give you, a land with fine, large cities that you did not build, with houses full of goods of all sorts that you did not garner, with cisterns that you did not dig, with vineyards and olive groves that you did not plant; and when, therefore, you eat your fill, take care not to forget the Lord, who brought you out of the land of Egypt, that place of slavery. The Lord, your God, shall you fear; him shall you serve, and by his name shall you swear.”

A man came up to Jesus, knelt down before him, and said, “Lord, have pity on my son, for he is a lunatic and suffers severely; often he falls into fire, and often into water. I brought him to your disciples, but they could not cure him.”

Jesus said in reply, “O faithless and perverse generation, how long will I be with you? How long will I endure you? Bring the boy here to me.” Jesus rebuked him and the demon came out of him, and from that hour the boy was cured. Then the disciples approached Jesus in private and said, “Why could we not drive it out?”

He said to them, “Because of your little faith. Amen, I say to you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”