"Truly I say to you that this generation will by no means pass away until all these things happen."
Which generation?
The one that sees "all these things".
Which things?
"Great tribulation."
It's not complicated.
The generation of Christians that sees the tribulation begin will survive the tribulation.
Why was Jesus telling us this?
Because the great tribulation is going to be so bad for Christians that we're not going to think any of us will survive it.
It's the same thing for women in labor. When you're in it, you don't think you're going to survive it. But most women do survive it.
"During that time Miʹcha·el will stand up, the great prince who is standing in behalf of your people. And there will occur a time of distress such as has not occurred since there came to be a nation until that time." (Daniel 12:1)
Daniel chapter 12 takes place in our day, not in the first century. It is in harmony with what is written in Matthew 24 about the fulfillment in our day:
"for then there will be great tribulation such as has not occurred since the world’s beginning until now, no, nor will occur again..." (Matthew 24:21,22)
When Satan is cast down from heaven, he will incite the UN to attack all religious institutions. It's going to look really, really bad for Christians. Jesus was telling us, when you see all these things going on, the appointed times of the nations to trample Christianity, don't freak out. It's going to be 3 1/2 years of it. Even though the religious institutions are going to be completely torn down, some individual Christians will survive and make it to the end of the 3 1/2 years of the great tribulation, the time when Christ will come on the clouds will great power and glory.
"Truly I say to you that this generation will by no means pass away until all these things happen."
Love for God and for each other will help us to endure.