The Bible gives us a clear answer. Paul came upon some believers in Ephesus who had been baptized by no less than John the Baptist. Yet they had not received the Holy Spirit for two reasons. One is that they did not have the laying on of hands. The other was that they apparently did not fully understand the Christian way of life, the covenant into which one enters through baptism.
What did their baptism by John accomplish? Undoubtedly, it helped prepare them for conversion, for he preached repentance. And it likely strengthened their resolve to obey God. But the baptism didn’t bring about their conversion or result in their receiving the Holy Spirit. Clearly, many factors have to be in order for that to take place, including knowledge of sin (the transgression of God’s law, 1 John 3:4), an awareness of the need for forgiveness, true repentance (turning from sin to obedience) and a clear understanding of the obligations of Christianity. In addition, the baptism should, under normal circumstances, be done by a minister of God’s true Church, followed by the laying on of hands and prayer to receive the gift of the Holy Spirit.
You can read this encounter in Acts 19:1-6, where you will see that Paul—after counseling the believers—baptized them again and laid hands on them.
Like baptism, the practice of laying on of hands has its historical roots in the Old Testament. In ancient times this practice, often accompanied by anointing with oil, was used to set men apart to serve God in the offices of king or priest. It was also sometimes invoked in setting apart sacrifices or other things for holy use. Similarly, laying on of hands after baptism signifies that the newly baptized person has now been set apart for God.
Since the days of the apostles, the laying on of hands after baptism has signified the actual moment of the receiving of the Holy Spirit and the setting apart of a convert as a child of God. It is only through the gift of God’s Spirit that we can develop the godly attitude of obedience and faith. The practice of laying on of hands for the receiving of God’s Spirit is mentioned in Acts 8:17; 19:6; and 2 Timothy 1:6.