Was the worship on Mount Gerizim from God or simply a man-made religion?
The worship on Mount Gerizim was not from God; it was a counterfeit, man-made religion. The northern kingdom established a secondary Temple worship there, but God's presence was not in it, and they failed to recognize that God dealt with Israel through Jerusalem.
Les explains that the Temple remained in the southern kingdom, Judah, and carried on as usual. The northern kingdom instead set up a secondary Temple worship on Mount Gerizim, creating its own counterfeit. The presence of God was not in it; it was just another man-made religion. This became the headquarters of their religion, and they did not recognize that God was dealing with Israel through the Temple in Jerusalem. Les further notes that all through Israel's religious history, Jerusalem is the headquarters of God's operation. The Samaritans asked, "What's the difference?" so God had to show the Samaritan believers that Jerusalem was the headquarters of God's dealing with the nation of Israel.