Mark 13:1 And as he went out of the temple, one of his disciples saith unto him, Master, see what manner of stones and what buildings are here!
The temple was made with marble stones, fifty feet by 24 ft by sixteen inches. It covered an area of five hundred yards by 400 yards. The dome was overlaid with gold. The temple was built under Herod's order and was the pride of the Jews.
Mark 13:2 And Jesus answering said unto him, Seest thou these great buildings? there shall not be left one stone upon another, that shall not be thrown down.
Rome would come against the people of Israel. They were not to destroy the temple, but when it caught on fire, the gold on the dome melted into the cracks of the stones. The armies tore the temple down stone by stone to get at the gold.
God allowed the temple to be destroyed because sacrifices were no longer to be done there. Jesus was the last sacrifice. The stubbornness of the temple leaders was also a reason. They destroyed the temple of God; Jesus. So God allowed their temple building to be destroyed. They wanted law and refused grace, so their covenant of the law, brought destruction because of sin.