In Matthew 11:20-24, Jesus denounces several cities for not believing the gospel though they had seen so many of his works. In each case he declares that unbelief in these situations will lead to a greater judgment than notoriously sinful Old Testament cities. The point being made is that rejection of the Gospel is the worst possible sin and will lead to the greatest judgment. Judgment will always be in proportion to the light and knowledge one has received.
Matthew 11:20-24