Thou hast neither part nor lot in this matter: for thy heart is not right in the sight of God. -- Acts 8:21 (KJV)
Simon believed. Simon was baptized. He stayed close to Philip and watched the miracles happen in front of him. Every visible box was checked. Then he pulled out money and offered to buy the power he had seen in the apostles' hands, and Peter answered without flinching: thy heart is not right in the sight of God.
A baptized believer, and something underneath was wrong enough for Peter to read it in a single exchange.
The Power Was Never the Problem
Simon wanted something real. He had spent years being called the great power of God, and when actual power walked into town, he wanted to hold it himself. Peter did not rebuke him for desiring the gift. He went after the reason for the wanting. Simon was chasing spiritual power so that people would go on thinking Simon was great.
That kind of hunger keeps a low profile. It comes to church, sings, gets baptized, and quietly bends everything holy back toward its own name. You can crave being the one with the answer, the one others come to, the one whose competence gets mistaken for calling. None of that prints on your face. You can run the whole play and look devout doing it.
Let Peter's Question Land
Acts 8 holds up a mirror that was never meant to flatter. It does not ask whether you want God to use you. Of course you do. It asks what you want the using for. Peter never tallied up Simon's conduct. He went straight past the behavior to the motive underneath it.
Picture Peter saying it to you this morning, naming the one thing in you that is not right. Pride, maybe. Envy. A craving for influence you have been filing under zeal.
Sit with whatever word he would use, and resist the urge to argue with it. Tomorrow's reading is where you do something about it.