Acts 8:16 For as yet He had fallen upon none of them. They had only been baptized in the name of the Lord Jesus.
Philip was going through Samaria telling people about Jesus and encouraging them to give their lives to Christ. He was baptizing them in the name of Jesus too.
But the Holy Spirit had not come upon them yet. They knew the word and they followed the teachings, but they knew they were missing something.
It was only when Peter and John also went to them and laid hands on them, praying for the Holy Spirit to come, that He did come into their lives.