Luke 23:31 is probably the least known saying of Jesus. He is speaking prophetically. It is a warning of judgment to come. He is addressing the women, the professional mourners, who generally appeared when there seemed no-one else to mourn for the condemned person. Jesus tells them not to mourn for him.
Jesus is the green sap filled wood approved of God the innocent one being unjustly condemned to death. By way of contrast Jerusalem and its inhabitants are the dry woods in rejecting the One sent to them to produce the fruit of righteousness by faith.
Nowadays, the word punishment has been dropped from many people’s vocabulary. Why is that? Surely if we do not find ourselves wishing to call down judgment of divine magnitude on some perpetrators of evil, this may reflect our ivory tower insensitivity, our good fortune in not being confronted ourselves by evil of such measure, or it may reflect our own moral indifference. Love and forgiveness of our enemies should not be invoked to sanction an easy and careless disregard or justice.