Jesus said there would be one sign. It would be to that ‘evil and adulterous generation’ It would be the sign of Jonah in the whale’s belly – a type of the death and resurrection of Jesus Christ. In other words, the only sign of God acting in mercy for that generation would be the death and resurrection of Jesus. That evil and adulterous generation rejection Jesus the Anointed One of God. The Old Testament speaks of the prostituion of Israel. She, Israel the nation, prostituted herself with idolatry. She went away from God, She crucified Jesus, the ultimate sin. She did not kiss the Son as in Psalm 2. So the Son was angry. Jesus, the Son judged her eventually. This was as the Son of Man who came as He said in Matthew 24, Luke 31, Mk. 13. She was adulterous as a nation – except for the small Remnant who were saved by the death and resurrection of Jesus Christ. For Christians, friendship with the world is enmity against God, James. He speaks of evil spirits. Peter said Christians having excaped the world if they again become entangled with the world will find themselves worse off. The world is full of evil spirits. So falling believers get worse evil spirits. Jesus said when a spirit (as all unbelievers have aplenty) leaves and returns to find it empty, he will bring seven more worse ones to inhabit that empty soul. Jesus kept casting out evil spirits from Hebrews/Israelites when He wa on earth. Israel the nation certainly had an emptiness and received many more worse evil spirits.