Why did Simon ask to buy the power to give the Holy Spirit?
Simon sought to buy the power to give the Holy Spirit for material gain, not spiritual concern. His profession was empty and his heart unchanged; he was a fake who saw only monetary reward and wanted what he could gain materially.
Les explains that Simon made an empty profession and went through baptism, but it was as empty as a bucket with no heart change. Simon said, "Let me have this, I'll buy it," asking for the power that on whomsoever he laid hands they may receive the Holy Spirit. Yet he was not concerned about the spiritual aspect of the Holy Spirit; all he could see was the monetary reward. Peter saw right through Simon and said, "Thy money perish with thee," showing that Simon was a fake, in it strictly for what he could gain materially. Even though verse 12 says he believed, Peter brings out the truth that it was not real belief.