Why did the Holy Spirit not descend on these recent believers in Samaria like He did on other believers in the Bible at the moment they accept Christ? Why did the apostles had to lay hands and pray for the Samarians to receive the Holy Spirit?
Acts 8:14 - 17
ESV - 14 Now when the apostles at Jerusalem heard that Samaria had received the word of God, they sent to them Peter and John. 15 Who came down and prayed for them that they might receive the Holy Spirit.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
One of the key verses in Acts is 1:8 where Jesus says, "But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth." The rest of the book tells the story of the expansion of the Gospel and the church. This verse 8:14-17 is the fulfillment of Christ's prophecy of the Holy Spirit spreading outside of Judea to Samaria.
The laying of hands was not necessarily "required" as it was not the case in Jerusalem (Acts 2) but rather Peter and John came who had ushered the first coming of the Holy Spirit and laid their hands on the Samaritan believers as a visible fulfillment of the gospel and the Holy Spirit crossing the ethnic boundary.
This is a unique time in history where the believers did not receive the Holy Spirit at the time of their belief. Acts 1:8 clearly states the Holy Spirit has yet to come. We see the coming in Acts 2 as the fulfillment of Jesus' promise. Likewise, the Samaritan believers also needed to receive the Holy Spirit after they believed in the gospel and were baptized.