While the slave girl was a slave to the spirit of divination that worked through her, and suppressed her identity, Simon Magus is in a far more dire situation, because his magical/occult involvement has actually blinded him to the completeness of his own entrapment. The light in Simon Magus was darkness* - he could no longer discern the difference between light and darkness, that is, between good and evil. Perhaps once, when he was a little child, he might have been able to, but now, Simon Magus was almost completely blind to the reality of his own nature and hardened to God's influence in his life.
But there was a man named Simon, who had previously practiced magic in the city and amazed the people of Samaria, saying that he himself was somebody great. They all paid attention to him, from the least to the greatest, saying, “This man is the power of God that is called Great.” And they paid attention to him because for a long time he had amazed them with his magic. But when they believed Philip as he preached good news about the kingdom of God and the name of Jesus Christ, they were baptized, both men and women. Even Simon himself believed, and after being baptized he continued with Philip. And seeing signs and great miracles performed, he was amazed.
Now when the apostles at Jerusalem heard that Samaria had received the word of God, they sent to them Peter and John, who came down and prayed for them that they might receive the Holy Spirit, for he had not yet fallen on any of them, but they had only been baptized in the name of the Lord Jesus. Then they laid their hands on them and they received the Holy Spirit. Now when Simon saw that the Spirit was given through the laying on of the apostles' hands, he offered them money, saying, “Give me this power also, so that anyone on whom I lay my hands may receive the Holy Spirit.” But Peter said to him, “May your silver perish with you, because you thought you could obtain the gift of God with money! You have neither part nor lot in this matter, for your heart is not right before God. Repent, therefore, of this wickedness of yours, and pray to the Lord that, if possible, the intent of your heart may be forgiven you. For I see that you are in the gall of bitterness and in the bond of iniquity.” And Simon answered, “Pray for me to the Lord, that nothing of what you have said may come upon me.” Acts 8:9-23
Just like the slave girl in chapter 16, I believe Simon Magus' identity was also stolen by this spirit of divination**, but what made it worse for him was that his evil-spirit-constructed identity as "somebody great" was affirmed by everyone in Samaria, from the least to the greatest, and what was even worse than that, Simon Magus' opinion of himself was perverted by blasphemy and false claims about God. He claimed to be "the Power of God that is called Great."
The affirmation by others of his false identity meant that his entrapment was far more complete. Being used to people's adulation towards him and affirmation of the falsehoods in his life was very bad for him. Such adulation is very dangerous to the recipient of it, particularly when it is mixed with claims about God's special approval. Such adulation should only be directed towards Jesus.
When he sees real miracles, Simon Magus is amazed, sees that they are superior to his own signs and wonders, for the miracles the apostles are doing are real miracles and not the lies and deceptions of evil spirits, and Simon Magus believes the gospel. But old self is not yet fully dead and gone (this is very common in new Christians! And old Christians too. Turning to Christ is a lifelong giving over of oneself to God). I think that secretly, Simon Magus still suspects he himself may be a "great man of God". His manner towards the apostles, overly familiar, tells us that he sees the apostles as something like colleagues, people who work in the same industry, fellow magicians.
On the seeing the Holy Spirit come down on his compatriots Simon Magus' true motive for all his prior deceptions becomes clear. As a magician he would have accepted monetary gifts, payment in return for 'readings', such people always do. In the early church, incidentally, prophets accepted no payment and the apostles too, they only accepted hospitality, food and board - while preaching they accepted no money. Monetary donations were made to the local churches to pay for the priest and distribute to the poor, donations were not made to the apostles, nor to prophets.
Simon Magus offers money to the apostles for this 'power' of bestowing the Holy Spirit- which shows how deeply he has misunderstood everything up to now.
The apostles were not magicians like Simon Magus had been - they did not work their own will, nor did they work for money, but the apostles were instruments of God's will - the Holy Spirit is one of the three persons of the Trinity, not merchandise - indeed, God is not an object to be bought and sold, but the Three Persons with whom every human being inherently has a relationship of complete dependence, the ens realism, the Ground of Reality. It is us whom Jesus Christ has bought, with his blood, on the cross, so that we belong to him, not the other way around.
The apostles rebuke Simon. The influence of the evil spirit that had worked through Simon Magus on his personality was still there. He was not quite right in the head yet - despite having been baptised and turning to Christ, Simon Magus' personality and beliefs and whole being were still perverted by his prior occult involvement and the beliefs that he had held about himself then. The gall of bitterness is the suspicion deep in Simon Magus' heart that no one would care about him without all the lies he wove about himself, the false reputation that he was a God's great power, the suspicion that no one valued him for himself, only for the fortune-telling and the occult 'favours' he provided.
The story of Simon Magus raises at least the possibility that even the person most deeply entrapped in false identities and occult involvement and greed, even a person who has misled others for money - Simon Magus misled a whole province with his lies and deceptions, even a cult leader, a false Messiah, someone who has blasphemed God by proclaiming that they are God's Great Power, even someone whose falsehoods are affirmed by many other people, even a person so blind that he would offer money in return for apostolic authority (something given freely by God that can never be bought and sold), even someone like Simon Magus can come to God and find salvation, albeit through a sharp rebuke.
After the rebuke, Simon comes to an attitude of humility and deference - he asks the apostles to pray for him - and this is a real sign of hope because up till now, Simon has only been full of himself and his own reputation. Now he is willing to acknowledge that others might know God better than he does, and that he himself might actually be in need of God's help, and that everything he thought beforehand about his own 'specialness' might be a lie. (This is not to say Simon is not special - he was a man for whom Christ died - in this respect he was infinitely special - but the whole Simon Magus, great man of God thing was a lie.) This is a big step and though we hear no more of this Simon in the New Testament, on the basis of this verse we might hope that this really was the beginning of Simon's walk with Christ, having Simon's permission, we might hope that God will continue dealing with him to bring him out of his entrapment to falsehood.
This Paragraph Added Sunday, and a few small edits made in previous paragraphs: Although it should be noted, some of the early Church Fathers tell a different story - according to Irenaeus, Justin Martyr, Hippolytus, and Epiphanius, Simon Magus did not ultimately reform himself, but ended up misleading people even more and being the source of 'all heresies.' Whilst it is not scripture, the uniform witness of these very early Christian writers, Irenaeus, Justin Martyr and Hippolytus ought to be taken fairly seriously. Perhaps this ought to be a warning to us, not to take lightly the moments when God's truth is presented to us, but to give God full permission to reign over our lives, lest we end up even worse off than we were before.
You see, unlike evil spirits, who inveigle, lie, and deceive their way into people's lives, God only comes into someone's life when they give him permission. God is the perfect gentleman in that sense. It is why true Christian conversion is usually such a large, visible turnaround in someone's life.
By the way (added afterwards) please note that Simon was already outwardly a Christian. Someone who is a Christian already might need God to turn them around, help them turn to him.
*re inner darkness - Luke 11:34-36: "Your eye is the lamp of your body. When your vision is clear, your whole body also is full of light. But when it is poor, your body is full of darkness. Be careful, then, that the light within you is not darkness. So if your whole body is full of light, and no part of it in darkness, you will be radiant, as though a lamp were shining on you."
**A note about transgenderism - interestingly these posts about possession bring to mind Walt Heyer's description of dissociative personality disorder - that is, the various female personalities suppressing his true self and trying to take control described in A Transgender's Faith, his autobiography p 92, p 104-106, p 110, etc, and such experiences are also recounted in many other places in the book. Walt's experience of the different female personalities trying to take control seems at least analogous to possession by evil spirits - I will not say that that is what it was - but if it was possession, then this whole subject is at least partly beyond the province of medical science. In the end it was God who delivered Walt Heyer and brought him back to himself, though one could say God used medicine to help him interpret and understand what had happened to him.
(We are incarnate creatures, and the physical and the spiritual in us are impossible to disentangle because we are each one whole person, not a separate spirit/soul and body.)
(Here is a theory - just as rain can be caused by God's intervention through prayer and the chance condensation of water in clouds - i.e. since God is the cause of everything, so intervention through prayer does not contradict physical causes - just so, for other spiritual influences there might well also be both physical and spiritual causes - dissociative personality disorder might well have a straightforward medical cause, childhood trauma or OCD might be an infection of the brain, but these things are also an expression of a malicious spiritual influence in that person's life. i.e. seek both medical and spiritual help if necessary. ) (There need be no guilt attached to this of course - in Christ there is no condemnation Romans 8:1)
Jesus, who is the Sun of Righteousness, brings healing on his wings.
But for you who fear my name, the Sun of Righteousness shall rise with healing in its wings. You shall go out leaping like calves from the stall.