Behold, I come quickly: hold that fast which thou hast, that no man take thy crown. Revelation 3:11
There are many passages in the gospels and revelation where Jesus promises to return and set up an earthly kingdom before all the apostles die. In sunday school, I was taught that the disciples falsely believed that Jesus would set up his earthly kingdom then and there. But, I wasn't told that Jesus (who some christians believe is God) thought he would be doing that too. Seems wierd to me that Jesus was God and knew all there was to know, but somehow got it wrong about the time he'd be returning to earth to smite all the evil-doers. Maybe "quickly" in Rev 3:11 means 2,000 to 3,000 years.
Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom. Matthew 16:28
I really don't see any other way you can interpret this verse other than the natural reading of it. I don't think that Jesus was talking about his ascension here. It's just not logical to think that Jesus meant that he'd go to heaven and not come back for a few thousand years when he said this. See also Matthew 23:36, Matthew 24:34, Matthew 26:64, Mark 9:1, Mark 14:62, Luke 9:27, and Luke 21:32.
Christians have been waiting for nearly 2,000 years for Jesus to return. They'll probably still be waiting for him in another 1,000 years. As a matter of fact, there has not been a year go by, since Jesus' death, that some group of christians somewhere didn't expect Jesus to return during their lifetimes.
I know there is a verse that says that even Jesus doesn't know when he'll return. (For the life of me, I can't find it at this moment.) That makes it even worse. If Jesus didn't know when he'd be returning, why would he have told his disciples that he was returning within their lives? Was he lying? Was it a "white lie" to give them hope? Isn't lying a sin? Did Jesus live a sinless life or not? Maybe, because he was God, he could lie and it wouldn't be a sin.
Well, I'll close this by saying, I'm done waiting. Now, I'm going to get on with my life and live it as comfortably and as fully as I can. I'm not going to waste my life waiting around for a 2,000 year old prophet.