I have never found anyone who adequately explained this message given by Jesus. It seems obvious to me that the first century church believed that Jesus would return during their life time. I suppose that many believed that Christ would return immediately after the destruction of the temple and of the nation. After Christ did not return they were forced to acknowledge that Jesus was speaking of two events, though they were written together in such a fashion as to make it appear as one. The secret to understanding Matt 24,Mark 13, and Luke 21 seems to me to be in learning to recognize the places where Jesus described the destruction of Jerusalem that occurred around 70ad and the places that describe Christ return and the end of the age. To make things more complex, it appears that some of the things that happened in 70ad may have something very similar to it happen at the end of the age. First, when Jesus told the apostles to flee to the mountains when they seen Jerusalem surrounded by armies...that happened in 70ad. There is a place in scripture where Jesus spoke of His return and he told the disciples not to flee or to try to save their life. So that is a clear difference. The 70ad Christians were to run for their lives, the end time Christians were to stand their ground(because the angels would gather them). I wonder how many differences others have noticed between the 70ad destruction and the end time destruction?