Vern Humphrey said:
Saint Augustine, who was a Manechean before he was converted to Catholicism, rejected belief in Satan and said evil sprang not from Satan, but was merely the absense [sic] of good.
I think you have the concept of evil and the identity of Satan confused. St. Augustine of Hippo theorized in “The City of God,” (New York: Marcus Dods Translation. Modern Library Publishers, 1950) that humans and angels are divided into two societies or “cities.” One serves God and is populated by the good angels and humans. The other opposes God and consists of fallen angels and evil humans. While evil may be defined as the absence of good, it is necessary for the existence of a greater good - free will. The fact that evil or sin is impersonal, however, doesn’t contravene the existence of Satan as an incorporeal yet existent personal being.
St. Augustine’s position is in accord with the
Catechism of the Catholic Church:
391 Behind the disobedient choice of our first parents lurks a seductive voice, opposed to God, which makes them fall into death out of envy. Scripture and the Church’s Tradition see in this being a fallen angel, called “Satan” or the “devil”. The Church teaches that Satan was at first a good angel, made by God: “The devil and the other demons were indeed created naturally good by God, but they became evil by their own doing.”
Vern Humphrey also said:
Satan comes from Rabbinical tradition, not from scripture.
The Apocalypse of St. John 12:7-9 has this to say about Satan:
And there was a great battle in heaven, Michael and his angels fought with the dragon, and the dragon fought and his angels: and they prevailed not, neither was their place found any more in heaven. And that great dragon was cast out, that old serpent, who is called the devil and Satan, who seduceth the whole world; and he was cast unto the earth, and his angels were thrown down with him.
St. John’s reference is by no means the sole Biblical basis for a belief in Satan. See also, e.g., Jude 1:6; Job 4:18: (“In his angels he found wickedness”.); Isaiah 14:12-15.