The apostles had learned a lot from Jesus in less than three years, but their training was not finished.  Jesus promised that the Holy Spirit would lead them into all truth (John 16:13), reminding them of what Jesus had already taught them (John 14:25-26), and showing them how to apply it in gospel mission (Acts 1:8).

Jews regarded Samaritans and Gentiles as less important to God.  But Peter and John went to Samaria when they heard that Samaritans had believed in Jesus through Philip's preaching.  When the apostles laid their hands on the new believers, the Holy Spirit filled them also (Acts 8:14-15).  God was showing the apostles that it was right for them to expect God's Word to work powerfully wherever they preached about Jesus irrespective of their religious background.

Encouraged by that, they continued to minister in Samaria.  As they made their way back to Jerusalem, they stopped in the villages en route and told more Samaritans about Jesus, who died as God's sacrifice for their sins and rose to life again.  The Holy Spirit was teaching them that preaching the gospel outside the church is a normal activity of the Christian Church; their commission was not only to people who already believed, but to take the good news to unbelievers … for them to hear the truth and be saved (Romans 10:13-15).

The gospel is God's powerful message about Jesus (Romans 1:16).  It leads people to conviction of sin, repentance, faith, baptism and discipleship (Acts 2:36-38).  And yet, today's church is often preoccupied with people already in the church - while ignoring Christ's commission to communicate the gospel with those who do not yet believe (Matthew 28:18-20).  The apostles knew that those ideas are wrong.  God does not only work within the context of church, but He uses gospel proclamation to unbelievers to draw them to Him.  So - wherever the Lord has called you to live, work or travel – share the gospel with whoever you meet and see what the Lord will do (Romans 10:17).