Why did Jesus say that without His death, burial, and resurrection there would be no salvation for the Greeks?
Jesus was anticipating the future outreach of the gospel to Gentiles. Salvation for Greeks/Gentiles required His death, three days and nights in the grave, and resurrection; apart from that finished work, they had no access to salvation. Gentile access was practically absent from Genesis 12 until Paul, except rare exceptions.
Les explains that unless Jesus died, spent three days and three nights in the grave, and was resurrected, there was no salvation for those Greeks. He was already looking forward to the time when the gospel would go to the Gentiles. Les notes that from Genesis chapter 12 until almost the Apostle Paul, practically no Gentiles had access to salvation, with exceptions like Nineveh, Ruth the Moabitess, and Rahab. Paul makes this plain in Ephesians 2:11-13, writing to the Gentile believers at Ephesus and in that area of the world.