What did Jesus mean by “green wood” and “dry wood?”

Answer:

"A great multitude of the people followed him, including women who also mourned and lamented him. But Jesus, turning to them, said, "Daughters of Jerusalem, don't weep for me, but weep for yourselves and for your children. For behold, the days are coming in which they will say, 'Blessed are the barren, the wombs that never bore, and the breasts that never nursed.' Then they will begin to tell the mountains, 'Fall on us!' and tell the hills, 'Cover us.' For if they do these things in the green tree, what will be done in the dry?"" (Luke 23:27-31).

As pitiful as Jesus' condition is as he was going to the cross, he was telling the women following him that they should actually weep for themselves and the coming generation. It would not be long before Jerusalem would be destroyed and that destruction would be far worse than the lone suffering of Jesus. See "The Fall of Jerusalem" for more details. Because of the severity of the destruction, Jesus states that many of them would have been better off never having children than to see their children die in that awful destruction.

Green wood still has the sap in it. The moisture prevents it from burning well. Dry wood has been cut and aged so that it burns very easily. Jesus is stating that if the Romans are willing to do this to an innocent man, what will they do to the Jews later on who are not innocent? His implication is that it will be much more severe.