From an RCG source:
“It’s the Days of my [Dave’s] Voice”
“Because I know what the "Days of my Voice" are. The Kingdom HAS to come as the "Mystery Goes Away," but I'm going to cover all of this. I'm going to drive it home and drive it home. It's prophesied over and over again. And I'm going to finish strong! And I want you to just be completely unable to get out of this, "this cell" I'm going to lock you in that God locked me in. I opened by saying, you know, I had to first be convicted and I am convicted, but that's fine for me, but I want YOU to be convicted. I want you to feel good all over. We've got to answer. Okay. Is there a difference between the "world to come" and "the end of the world?" How about that? What about "lands" and "houses?" We've got to go back to a lot of different things here, and they're all neat and they're all fun and they're all just, wow, they're easy now….
...Now ask yourself, If God had made this plain wouldn't, the whole world have known his plan? He didn't want them to know it, He wanted it to be a "mystery," including even to his people, because at the very end of the age, a lot of them would be doing a lot of things, they shouldn't have been! They would have been watching, when He wanted to see what their attitude was, but he had this little "micro-flock" who would kind of get things ready in a very difficult time. Not in the Philadelphian era, I mean, five years before Mr. Armstrong died, I heard him say he wrote it and said it, in a sermon that 30,000 people had already left the church five years before he died. So there's nothing new under the sun. All kinds of people have left the church down through the ages. So if people stopped leaving the church here, you almost have to wonder what's wrong. So people, you know, people leave and that's the way it is, but more come than leave. And that's good. Unless you have an apostasy. It blows everything to pieces as happened in the first century, happened in the 20th, and no doubt other times. So that's very helpful.”
Comment: The “Mystery” he references is his “truth of prophecy,” in his series. For starters, the mystery/confusion only is getting worse in RCG and secondly, biblically, the “Mystery” was revealed to Christians 2,000 years ago (noted in Colossians 1:26-29, Ephesians 1:9-12, Ephesians 3:3-7) as salvation through the work of Christ which was going out to the Gentiles. Not sure how there is room for another mystery or why Dave’s mystery is greater than Christ’s?