What did God have to show the Samaritan believers in Acts?
The Samaritan believers needed to learn that Jerusalem was the headquarters of God's dealing with the nation of Israel, not Mount Gerizim. Their counterfeit temple worship on Mount Gerizim was man-made, but God's true operation centered on Jerusalem, where He dealt with His people under Judaism.
Les explains that the northern kingdom had set up a secondary Temple worship on Mount Gerizim, a counterfeit where God's presence was not. The Samaritans did not recognize that God was dealing with Israel through the Temple in Jerusalem. Because of that historic mentality, God had to show these Samaritan believers that Jerusalem was the headquarters of God's dealing with the nation of Israel. Les also notes that under Judaism Jerusalem was where God dealt with His people, but the New Testament Church has no earthly headquarters; it is headquartered in heaven. Antioch was a fountainhead for the Gospel to the Gentiles, yet Scripture never places Antioch or Jerusalem as the Church's headquarters.