Matthew 23:36

“Truly I say to you, All these things will come on this generation.”

Jesus then makes clear quite forcibly (truly I say to you) that what He has been speaking about (their blood coming on them) will come on the present generation. He knows, as He will shortly explain to His disciples, that after His death God's judgment will come on Jerusalem, and that that will include all the effects of a major invasion which would set alight the whole of Palestine, beginning in Galilee.

For the importance Jesus places on ‘this generation' as the generation that faced its greatest opportunity and blew it see Matthew 11:16; Matthew 12:38; Matthew 17:17. Above all other generations it proved its unworthiness, for it was the only generation in history that had witnessed God made man walking among them. It stands for ever against the lie that if only God would reveal Himself we would believe.