God forgave the Ninevites based on their sincere repentance, without requiring vicarious sacrifices, which shows that Jesus' death wasn't necessary for salvation.

The argument begins by acknowledging the Muslim claim that the Ninevites were forgiven solely based on their repentance. However, this interpretation overlooks the broader biblical context, particularly the sacrificial system that was in place at the time. In the book of Jonah, it is evident that God’s acceptance of the Ninevites' repentance was made possible by the vicarious sacrifices being offered in His holy Temple in Jerusalem. Jonah's prayer and his commitment to offer sacrifices upon his deliverance further underscore this point. Moreover, the previous chapter of Jonah illustrates that the people of Nineveh turned to God in faith, but this act of repentance was not isolated from the sacrificial system that God had established. The sacrifices served as a means of atonement, which is a crucial aspect of God's plan for redemption throughout the Scriptures. Thus, the argument that God can simply overlook transgressions without a sacrifice contradicts the foundational teachings of both the Old and New Testaments regarding the necessity of atonement for sin. In conclusion, while the Ninevites' repentance was significant, it was the sacrificial system that allowed for their forgiveness, emphasizing that God's justice and mercy are fulfilled through atonement. This principle is consistent with the Christian understanding of Jesus' death as the ultimate sacrifice for humanity's sins, reinforcing the necessity of substitutionary atonement for salvation.