I can't explain to you because you come across as ignorant. If your truly interested then read the prophecies.
I was raised a Roman Catholic son, I know my Christianity. It's a nice story book, like Lord Of The Rings, but with more fantasy.
You will understand what Jesus did and why.
I know what the Bible says he did, and the reasons the Bible gives for him doing it. Reality: He didn't die for 3 days and come back to life. He didn't ascend to heaven. There is no empirical evidence of pre and post sacrifice levels of sin across the universe. Even if it had fallen, correlation is not causation.
The "how-it-works" part of it is irrelevant.
You call me ignorant then willfully ignore the desire to explain something fantastical? You do me a disservice good sir!
C.S Lewis explained this perfectly. He said people were eating healthy foods long before the idea of vitamins came along, and people will continue to eat healthy foods after vitamins have disappeared.
Sure, if you want to completely ignore all the really unhealthy things people did, like wearing lead-based makeup. Hell, they couldn't even reliably cure leprosy back in Jesus' time! Modern medicine can, 15 million people cured (and counting).
All we know Jesus' death has made us right with God. It works. That's the bottom line.
Jesus didn't stay dead. Why not? Surely that would have been a greater sacrifice? Or is 3 days 'enough' of a sacrifice? Why 3 days? Loads of people have been dead much longer than 3 days! Can you point to any scientific studies outlining the precise effects of Jesus' sacrifice so we can test it please?
As for your obvious mocking of Jesus ascending into heaven, again, if you actually did a bit of research and read the prophecies you would understand why.
Why not operate an open door policy? Surely he can see people are doing good on Earth right now? Why doesn't he lend them a hand? It's not like Heaven can get full is it? Everyone nice should be up there! Why are we even down here when God already knows who is good and who is evil?
The stage is not yet set for his return, but it is building. Prophecies are being fulfilled right now.
I'll put the kettle on. What's building by the way? He's a carpenter so I'm gonna guess it's a REALLY big staircase.
Edit: Apologies to JoeF1, misquoted you.