As the apostles remark on how great the temple is, Jesus immediately pops their bubble. The whole place is coming down, and other people will claim to be the Messiah. That is exactly what happened. In 70 AD, the Romans destroyed the temple. Popular rabbis of the time would proclaim others to be the Messiah. These were foretold to the apostles so that they would be ready, and so that they would not be enticed to leave the way that Jesus taught them for the other options coming down the line. The legacy we have been given by generations before is a testament to the enduring church built by our Savior, built on his solid foundation.