How do we know that God judges people for their unbelief?

The Scriptures provide a clear testimony that God judges those who do not believe in Him, as exemplified in the events surrounding the Israelites after their deliverance from Egypt. Jude references this when he notes that God saved a people but subsequently destroyed those who did not believe. This principle is not confined to the Old Testament; the New Testament also affirms that faith is essential for pleasing God. Unbelief ultimately leads to God's judgment, echoing the warnings from the past that unbelief can lead to eternal condemnation, just as the cities of Sodom and Gomorrah suffered due to their rebellion against God's design.