This is commentary on Acts 8:15,16 by Chuck Smith that I found and thought it is worth sharing here:
Who were, when they had come down, prayed for them, that they might receive the Holy Spirit: (For as yet he was fallen upon none of them: only they were baptized in the name of the Lord Jesus.) (Act 8:15-16)
Now it is interesting how that this has been a problem to so many Bible commentators. The fact that they had not yet received the Holy Spirit. That He had not fallen upon them as yet. It is commonly acknowledged that a person is baptized by the Spirit into the body of Christ. And no man can call Jesus Lord, except by the Holy Spirit. And the moment a person receives Jesus Christ and is baptized, the Holy Spirit comes into their lives. We know that you cannot receive Jesus without receiving the Holy Spirit into your life. And so this poses a great problem to the majority of Bible commentators when we find that the people in Samaria had believed and were baptized in water, and yet, the apostles sent them down that they might receive the Holy Spirit, for He had not yet fallen upon any of them. I am surprised that with all of these scholars, who are so problemed over this particular text, that they have not noted the Greek preposition. You remember Jesus said concerning the Holy Spirit to His disciples, "For He is with you and shall be in you." But later Jesus said, "You will receive power when the Holy Spirit has come upon you." Now this is the same Greek preposition epi that is used here. The Holy Spirit had not yet fallen, epi, upon them. So the commentators have difficulty trying to say, "Well, they were not filled with the Spirit; this was some special case in Samaria, because this was the first time out of Jerusalem and all." And they really wrestle and do all kinds of foolish things with this text. Because they do not want to acknowledge that there is an empowering experience of the Holy Spirit apart from conversion. But yet, that is exactly what the text does prove. That yes, we do receive the Holy Spirit in us when Christ comes into our lives. But there is an empowering experience subsequent to our salvation, where our lives are endued with the power of God's Spirit, as He comes upon us, anointing us for power to serve God. And it's a very simple, obvious solution, but it is one that most of the Bible commentators really stumble heavily over this. And I am amused at the various explanations they try to give of this particular text when the answer is so simple.
They had received Jesus Christ; they were baptized, so obviously the Spirit was dwelling in them. But they had not had an empowering experience like the apostles experienced on the day of Pentecost. For He was not yet fallen upon any of them, only they were baptized in the name of the Lord Jesus.