Father Salvador Carrillo, a Scripture scholar comments- "Satan's greatest victory is that he has got us to believe that he doesn't exist, thus permitting him to act with complete freedom.
Satan uses three methods: oppression, obsession & possession.
Oppression is the effect of Satan on bodies and things, for example, noises in the night, things that move about themselves, lights that go on and off, voices, some illnesses that are medically in explicable.
There was a man named Julio Nunez who was unable to walk and had to go around on all fours. The Lord healed him at a prayer meeting. About a year later, the parish priest of San Francisco de Macoris asked us to give a charismatic retreat. I invited Julio to come to the retreat to give his testimony.
When I arrived and asked for Julio, a lady sadly told me: "Father, that thing came back to Julio. Yes, Father, he can't walk anymore and is back to crawling again."
"How long has he been like this?"
"It started again five days ago." I asked her to go and find him, and he was brought to see me on a horse. We began to pray for his healing. I said to the Lord: "Lord , you can't show up badly here, this is Julio's parish,"but the Lord didn't heal him. So we began to pray in tongues, suddenly the word's "spirit of illness"came to my mind. So I commanded:"Spirit of illness, in the name of Jesus I order you to come out and let this child of God be free. In the name of Jesus I order you to throw yourself at the feet of Jesus, so that he may dispose of you as he sees fit, and I forbid you to return and bother him, for he is a child of God and you own no part of him."
Julio started shivering, and then, very simply, he got up and started to walk.
Obsession is the influence and the action of the enemy over people's minds. There are people who are tormented by a tremendous sexual obsession or the idea of suicide; by a spirit of blasphemy or self destruction or contempt: by the feeling that they are not worthy of God's forgiveness. It could be said that an obsession is like a temptation, except that instead of being temporary it is permanent, and has a power and an intensity that seem to make it impossible to overcome.
Possession occurs when a person has made a conscious act of giving his will to Satan, selling his/her soul, signing satanic pacts with blood or belonging to a satanic sect. It can also occur in people whose parents have consecrated them to the devil with or without their consent.
(extract taken from the book-Jesus Lives Today by Fr Emiliano Tardif)