Scriptures are taken from the New American Standard Bible.

On His way to Calvary, exhausted and already bleeding from many wounds, Jesus must have drawn pity from any in the crowds who had tender hearts.  Women customarily followed those doomed to crucifixion on their way to execution, wailing.  They often offered the victims a mixture of wine mingled with myrrh, which would lessen their pain.  (We know from Mark 15:23 and Matthew 27:34 that Jesus refused this drink when it was offered before his crucifixion.) 

Jesus knew He had come to earth for this very purpose – to suffer as the Lamb of God to take away the sin of the world.  His agony had only begun, but He knew that when His great sacrifice was faithfully accomplished, it would result in life for the whole human race; and He would be reunited with His Heavenly Father.   It was "for the joy set before him" (Hebrews 12:2) that He was able to endure the cross.  Thus spiritually strengthened, He was able to turn His attention to the women following Him and sorrowfully warn them of the suffering that faced them when Jerusalem would be besieged.

On what is now referred to as Palm Sunday, as Jesus had "approached Jerusalem… He [had] wept over it, saying… 'the days will come upon you when your enemies will… hem you in on every side, and they will level you to the ground and your children within you… because you did not recognize the time of your visitation.' "  (Luke 19:41-44)  And a few days later He had said, "when you see Jerusalem surrounded by armies, then recognize that her desolation is near…. Jerusalem will be trampled under foot by the Gentiles until the times of the Gentiles are fulfilled." (Luke 21:20-24, italics added) 

In reference to verse 31 of Luke 23 – "For if they do these things when the tree is green, what will happen when it is dry?" – Jesus had pronounced Israel's rejection from God's favor only days before.  If the nation could carry out this act of gross injustice while it still retained some of  its religious vitality,  what could be expected of it as time wore on and its religious vigor "dried out"?  As history verifies, the "wood" would be ready for "burning" – complete destruction.

On a side note:  Israel was rejected for refusing to recognize their Savior.  But as Luke 21:24 (above) states, the rejection would last only until the times of the Gentiles would be fulfilled.  The Apostle Paul wrote, "…a partial hardening has happened to Israel until the fullness of the Gentiles has come in; and so all Israel will be saved…" (Romans 11:25-26, ital. added)  We can see the beginnings of Israel's restoration in its becoming a nation again.  And in God's due time, the Jewish nation will say, "Blessed is He who comes in the name of the LORD."  (Matthew 23:39)