What does Matthew 24:2 mean?

Jesus and His disciples have left the temple after an extensive time of teaching. That included a severe rebuke of the scribes and Pharisees (Matthew 23:13, 15, 16). It ended with Jesus mourning over Jerusalem's refusal to recognize and receive Him. As a result, He is abandoning the city, removing Himself from the role of its protector (Matthew 23:37–38).

For some reason, the disciples pointed out some of the buildings of the temple. They might have been commenting on their beauty, since at that time the temple complex was newly renovated and impressive. They might simply have been making small talk as they traveled. Either way, Jesus takes advantage of the moment to reveal more detail about the coming judgment of God on Jerusalem and Israel.

First, Christ makes it clear he's referring to the temple buildings they are all looking at. He is not speaking in parable, or symbolism, or talking about some other location. The prediction He gives is dire: the entire structure will be obliterated, down to the foundations. Jesus is predicting the utter destruction of the historic and beautiful temple of Israel (Mark 13:2).

This prophecy of judgment was completely and fully fulfilled when Rome destroyed Jerusalem in AD 70. In response to a Jewish revolt, the Roman Empire laid siege to Jerusalem for five months. At the end of this time, the city was invaded and ransacked, bringing the Jewish death toll into the hundreds of thousands. Romans burned the temple, causing leftover gold to melt into the cracks of the masonry. To remove it, soldiers literally tore the structure apart brick-to-brick, leaving nothing but the level foundation. At that point, Jesus' prophecy was fulfilled, and the Old Testament system of sacrifices had entirely ceased to be (Hebrews 8:13).