Though Ezra 4:3 mentions a political reason as the primary motive for why the leaders of Israel refused their help, no doubt they had a deeper motive for why they did so. The leaders of Israel knew that these people did not worship the Lord because they believed that he alone was God, they worshipped him because they thought he was one god among many. The Lord demands exclusive worship and the people of Israel are unwilling to allow people that want syncretistic worship to have any part in their community.1
3 But Zerubbabel, Jeshua, and the rest of the heads of fathers’ houses in Israel said to them, “You have nothing to do with us in building a house to our God; but we alone will build to the LORD, the God of Israel, as King Cyrus the king of Persia has commanded us.”