This one is the key to everything. It was the most radical breakthrough in human thought since Abraham discovered that G_d was playing the universe interactively. This discovery was made by the supreme kabbalist, the Arizal (Rabbi Isaac Luria, 1534–1572) and it changed the way everyone thinks to this day.
Here's what I mean: Until the Arizal came up with this, the classic version of world theo-history was, "G_d made a nice world, but we messed it all up. So now, you better be good, because boy is He going to give it to those who made this mess."
Then the Arizal comes and turns everything upside down: "The whole mess is G_d's fault. He had a great idea, but it came out a big mess. And He put us here to clean up the mess and get His dream working."
Get it? In scenario A, G_d is the active party, and we are entirely passive. In scenario B, it's all up to us. That's a major revolution.
This idea is called tikun, meaning "fixing." The Arizal and his students spoke about every mitzvah as a way to fix something in the universe. Remember those nuggets of gold in The Gold Mine episode? Or the pearl in Deep Sea Diving? Those are references to the sparks of luminous vessels that feel from the primal world of Tohu.
Hey, why re-explain the whole thing here? Read Fallen Sparks and you'll get the whole idea. And then you'll see that just about everything we have to say about the world today is in the shadow of the Arizal's Big Idea.