Satan in the Gospels
If you believe in Christianity, you have to believe existence of God, the Holy Ghost, and Christ Jesus as well as Satan, since God sent the Holy Ghost and His Son, in the form of Christ Jesus, to the human world to fight against Satan.
Indeed, the Gospels mention Satan:
Matthew 4:10 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.
Matthew 12:26 And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?
Matthew 16:23 But he turned, and said unto Peter, Get thee behind me, Satan: thou art an offence unto me: for thou savourest not the things that be of God, but those that be of men.
Mark 1:13 And he was there in the wilderness forty days, tempted of Satan; and was with the wild beasts; and the angels ministered unto him.
Mark 3:23 And he called them unto him, and said unto them in parables, How can Satan cast out Satan?
Mark 3:26 And if Satan rise up against himself, and be divided, he cannot stand, but hath an end.
Mark 4:15 And these are they by the way side, where the word is sown; but when they have heard, Satan cometh immediately, and taketh away the word that was sown in their hearts.
Mark 8:33 But when he had turned about and looked on his disciples, he rebuked Peter, saying, Get thee behind me, Satan: for thou savourest not the things that be of God, but the things that be of men.
Luke 4:8 And Jesus answered and said unto him, Get thee behind me, Satan: for it is written, Thou shalt worship the Lord thy God, and him only shalt thou serve.
Luke 10:18 And he said unto them, I beheld Satan as lightning fall from heaven.
Luke 11:18 If Satan also be divided against himself, how shall his kingdom stand? because ye say that I cast out devils through Beelzebub.
Luke 13:16 And ought not this woman, being a daughter of Abraham, whom Satan hath bound, lo, these eighteen years, be loosed from this bond on the sabbath day?
Luke 22:3 Then entered Satan into Judas surnamed Iscariot, being of the number of the twelve.
Luke 22:31 And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat:
John 13:27 And after the sop Satan entered into him. Then said Jesus unto him, That thou doest, do quickly.
However, driving out Satan from people is an act most difficult to be understood by modern people, since they live in the modern world supported by advanced science and technology. Nonetheless, there is a rule and traditions of exorcism in the Vatican:
The Catechism of the Catholic Church states: "When the Church asks publicly and authoritatively in the name of Jesus Christ that a person or object be protected against the power of the Evil One and withdrawn from his dominion, it is called exorcism."https://en.wikipedia.org/wiki/Exorcism_in_the_Catholic_Church#Notable_examples
So, the Christian churches are partly based on recognition of Satan. But as God cannot be seen, Satan cannot be seen, neither. So, anybody, including Christian priests of any schools, who cannot believe in what cannot be seen does not believe existence of Satan as well as God. But most people who do not believe in both God and Satan are often under strong influence of Satan. One example is Hitler.
Christ Jesus never tried to dive Satan out of priests of the Jerusalem Temple, Herod and other enemies, although He drove Satan out of some individuals. It might suggest that Christ Jesus was not God but just His Son.
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Luk 5:14 And he charged him to tell no man: but go, and shew thyself to the priest, and offer for thy cleansing, according as Moses commanded, for a testimony unto them.
Luk 5:15 But so much the more went there a fame abroad of him: and great multitudes came together to hear, and to be healed by him of their infirmities.