You had some kind words the other day for old father Abraham. I'm convinced he's one of the great saints, a religious genius and Close Personal Friend of God whose Semitic desert hospitality welcomed the triune God in the stranger and pleaded for the lives of sinful men.
For his faith in the Unity of God, Satan despises Abraham and for his sake his descendants -- Jew and Arab alike -- whom he seeks to destroy: the first (and Christians, their younger brothers) through a failure of faith (idolatry, whether in the worship of golden calves or in atheism or the nation state), the second through a disordered and fanatical misapprehension of faith as incitement to jihad. In the end, it all comes down to a realization that the real Enemy is not one man or another, but the Evil One, whose hatred is for Abraham's knowledge of God as One -- and thus to the central and salvific importance of Unity. Think of it, if you like, as Satan's riff on the doctrine of Original Sin.
As O'Connor says, if the evangelists included the demons' remarks in scripture, it's because they reckoned their remarks about Jesus were "pretty good witness."