Satan’s greatest triumph is making people think he doesn’t exist.
Look to your Bible, as other posters have pointed out.
(Mat 4:1-10) Then was Jesus led up of the Spirit into the wilderness to be tempted of the devil. {2} And when he had fasted forty days and forty nights, he was afterward an hungered. {3} And when the tempter came to him, he said, If thou be the Son of God, command that these stones be made bread. {4} But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God. {5} Then the devil taketh him up into the holy city, and setteth him on a pinnacle of the temple, {6} And saith unto him, If thou be the Son of God, cast thyself down: for it is written, He shall give his angels charge concerning thee: and in their hands they shall bear thee up, lest at any time thou dash thy foot against a stone. {7} Jesus said unto him, It is written again, Thou shalt not tempt the Lord thy God. {8} Again, the devil taketh him up into an exceeding high mountain, and showeth him all the kingdoms of the world, and the glory of them; {9} And saith unto him, All these things will I give thee, if thou wilt fall down and worship me. {10} Then saith Jesus unto him, Get thee hence, Satan: for it is written, Thou shalt worship the Lord thy God, and him only shalt thou serve.
Here is the narrative of the temptation of Jesus in the wilderness. Notice the personal pronoun “him” used in verses 7, 9, & 10. The word “him” is the word “autw” (auto) which is the same word used 3 times. It is a personal pronoun, singular and in the dative case. The dative case may also be referred to as the case of personal interest. In the three instances above it is used to express to whom or for whom the action of the verb is done. So we see in the 3 verses the words “said” and “saith” which are two verbs denoting action. We can also plainly see that the devil is the recipient of the action of those verbs. If Satan does not exist, then who was Jesus speaking to? His flesh? Impossible because the grammar will not allow it. The words of Jesus were aimed right at Satan and because the dative is used in this case, he was speaking to another being. The three uses of “him” are also singular which means the words of Christ were aimed at a single person.
In verse 3 we have the same scenario with the same word except for one difference. This time the tempter came to Christ, “to him.” So here the tempter was speaking to Christ which means, by the dative again, we have a dialogue taking place between two persons, Christ and Satan. Therefore, if someone wants to deny the existence of Satan, they must definitely cut the temptations of Christ out of their Bible.
(Mat 12:26) And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?
If Satan does not exist, then how come the Bible is very explicit stating that Satan has a kingdom. The word “his” is the same word as we saw in Matthew 4 except this occurrence is not in the dative it is in the genitive case which shows ownership or possession. You see the personal pronoun is used here instead of the antecedent noun “Satan.” The word “himself” is also a personal pronoun except this word is in the accusative case which normally shows who is the receiver of the action of the verb. Both “cast out” and “divided” are the verbs in question with “himself” as the receiver of the action. So here we see that if Satan’s kingdom is divided or he casts himself out, his kingdom will fall. This language tells us we are dealing with a bona fide kingdom and not a mythological or medieval invention.
Finally, this is taken from an interview with Father Gabriele Amorth, an exorcist in Rome, originally published in the June 2000 issue of 30 Days, an Italian Catholic publication.
Q. But if one does not believe in the existence of Satan, does one’s faith remain intact, is it still the Catholic faith?
Fr. Amorth: No. I will tell you a story. When I met Don Pellegrino Ernetti for the first time, a celebrated exorcist who had practiced in Venice for forty years, I said to him, “If I could speak to the Pope, I would tell him that I meet too many bishops who do not believe in the devil.” The following afternoon, Father Ernetti came back to see me to tell me that that same morning he had been received by John Paul II. “Holiness,” he had said to him, “there is an exorcist here in Rome, Father Amorth who, if he met you, would tell you that he knows too many bishops who do not believe in the devil.” The Pope answered him briefly: “***He who does not believe in the devil does not believe in the Gospel.”