And when the devil had ended every temptation, he departed from him (Jesus) until an opportune time. Luke 4:13 (RSV)
Then Satan entered into Judas called Iscariot, who was of the number of the twelve; he went away and conferred with the chief priests and officers how he might betray him (Jesus) to them. And they were glad, and engaged to give him money. So he agreed, and sought an opportunity to betray him to them in the absence of the multitude. Luke 22:3–6 (RSV)
No one in possession of a sane mind will deny that there is evil. It is so manifest at times that the whole world will agree on the evil. At times evil is so subtle that it completes its goals nearly unnoticed. Our eyes behold it displayed in the words and actions of others. We, at times, must painfully confess the evil that lives within our hearts.
Scripture does not shy from the reality of evil. Neither does it pretend that evil is not a physical being: scripture names it Satan, the evil one, the devil, a fallen angel. Jesus was clear that the devil is a reality whether we 'modern' humans wish to acknowledge it or not.
Whence evil has come into the Father's creation is not mine to know. It is here, raging against the Father and all that He has created. The devil would undo all things to smite the Father and is mad with hate that he cannot. We pretend at our peril that this is not so. The devil's hatred of the Father is such that he will visit it on us whenever he can.
Failing to tempt Jesus, the devil departed, until an opportune time, as St. Luke records it. He will bide his time, and then he will act. Something in Judas faltered as he followed Jesus, and the evil one was there, giving birth to the betrayal of Jesus. Perhaps Judas no longer trusted Jesus, seeing Him as a threat to God's people, or he was tired of walking all over Judea or frustrated that the Messiah had not lived up to his expectations.
The devil could not care one whit what was in Judas' heart. Judas was a tool to wound the Father, nothing more or less. Judas, the priests and officers of the Temple all sold themselves for thirty pieces of silver. Once used, the evil one abandoned them all to despair and hopelessness.
The devil is incapable of learning, of realizing that nothing he does will defeat the Father. He has and will continue to do as much harm as possible, thinking that he will one day succeed against God. He is a defeated fool. Like Hitler in his bunker in the last days of WWII, commanding armies that no longer existed, willing to let all of Germany die for his failures, sputtering out hate to the very end, the devil's hatred drives him.
The sad truth is that the Father would forgive and welcome this fallen angel in the Kingdom. If the devil asked for the mercy of God that flows from the Father's heart, it would be given. Should the time come from his heart, the devil would confess: 'Jesus is Lord,' He would enter paradise like the repentant thief.
Here we would do well to remember that this same love and mercy is ours every day. There is no sin He will not forgive, no failure so massive nor rebellion so deep within us, that He will not forgive. The Father desires that we do what the evil one cannot do and confess our sin's truth. He would have us repent from all that leads to death to discover our true life in Jesus, our Lord.