Why was God so harsh with those in idolatry?
We must understand that God dealt very harshly because it was through the people of Israel that the Messiah would later come. Satan, in his perpetual effort to oppose God, sought to have the people of God fall into false worship and through intermarriage with other people to destroy the messianic line and make not only the promises of God null and void but also destroy means by which the Messiah could be born. If this could be accomplished, then none would have any hope of deliverance from sin. Therefore, we see in the Old Testament God being very harsh and strict according to the Law.