“Anyone who has ears had better listen!” See commentary on Matthew 11:15. This is the same Greek phrase. Jesus has just finished teaching that wicked people will be burned in Gehenna, while godly people will live and shine in the Kingdom of God. This is not mere threats. There will be a Judgment and unsaved people will be annihilated in Gehenna while saved people will live forever. Everyone better listen and pay attention.
[For more on annihilation in Gehenna, the Lake of Fire, see commentary on Rev. 20:10.]