what was the point of the cube?

It's funny. The explanation to some is given in the movie. People just don't like to accept it. they expect some design or motivation. That's what we expect from the world but the scary truth is we are at the mercy of the systems we have created. The world doesn't work the way we expect. There is no grand design, no master plan, or big conspiracy.

The idea is essentially you have a system in this movie that has run amok. The left hand doesn't know what the right hand is doing... except there are many hands, not two. People are all working on parts of it and no one understands the whole. Who puts them in there? Some employs working for some firm hired to work on a big project kind of like Worth was just some random employ who designed a small portion of it.

Straight from the movie itself:

-Holloway, you don't get it.

-Then help me, please, I need to know.

-This may be hard for you to understand, but there's no conspiracy. Nobody is in charge. It's a headless blunder operating under the illusion of a master plan. Can you grasp that? Big brother is not watching you.

-What kind of f_____' explanation is that?

-It's the best you are gonna get. I looked, and the only conclusion I could come to is that there is nobody up there.

- Somebody had to say yes to this thing.

- What thing? Only we know what it is.

- We have no idea what it is.

- We know more than anybody else. I mean, somebody might have known sometime before they go, they got fired, or voted out, or sold it, but if this place ever had a purpose, and it got miscommunicated, or lost in a shuffle. I mean, this is and accident, a forgotten perpetual public works project. Do you think anybody wants to ask questions? All they want is a clear conscience, and a fat paycheck. I leaned on my shovel for months on this one. This was a great job!

-Why put people in it?

-Because it's here. You have to use it or you admit it's pointless.

-But it is pointless.

-That's my point.

I read it basically as a meditation on prisons. It probably comes from Fouchault and the other Euro Left philosophy, note all the references to 'the system.'

For example they don't know who built the cube, just as we don't know who invented the prison. Who first had the idea that criminals should be punished by geographical confinement? No one knows.

Didn't read other posts so my idea might not sound original:

The cube is a metaphor for Earth or the Universe and we humans on it. We don't know where we came from, who created it, what we are doing here. We just appeared here with no specific reason. The cube is there for no specific reason, it's just there and there's people on it.

Some of them have theories of a meaning, and want to believe there is one.

We can't take the sequel/prequel into consideration for explanation. They were made just to make money on the initial idea.

POINTLESS STORY, POINTLESS MOVIE. Much like a Soccer game, all ebb and flow, back and forth, and no scoring. I want to sue for my time back. BORING.

There is no reasonable explanation. The initial movie was entertaining but it's clear that the writer/director had no clear explanation and that the Cube merely served as a plot device for a rather intriguing movie. Once the sequels came out it's clear that they scrambled to come up with some poorly thought-out reason for the Cube, which makes zero sense.

The director made a short film showing what was beyond the bridge, but later destroyed it.

The sequels, which aren't canon in my opinion, eventually explain everything, but poorly. They leave more unanswered questions and it's quite sloppy.

Massive spoilers for the trilogy below:

Hypercube and Zero both explain that the government or government like agency is responsible for the construction and usage of the structure. Zero further explains that people are placed inside for having done something against the government or are wards of the state to some extent. Zero further explains, in a very fanfiction type way, that everyone inside consented to being placed inside, but have no recollection of it. This is done badly in writing, but it helps clear up why some of their memories are hazy and fuzzy, where as some are fine and others can barely remember their own name.

In Hypercube; an engineer who build the technology for the touch doors, two former employees of the organization (one is an almost senile mathematics professor of some kind) and an intelligent (but blind) computer hacker are just a few of the people placed inside. With Zero, one of the people inside was a political protester. Zero has a lot of weird issues, one being that they have robotics technology or kill drones (think Terminator) that are generals that are placed inside to keep people from reaching their goals or are outside the structure to keep them from getting away. It's cheesy and stupid, but perhaps it explains more about Quentin's volatile behavior.

Regarding where Kazan went, it's one of two possibilities. He either safely crossed the bridge and found his way to the exterior of the shell; taking him outside to the woods. Another being that he ended up like someone who tried to escape; being taken to a dark room and being asked a series of questions--where if he guessed wrong, he would be killed.

A popular theory is that Kazan was a former employee of the group behind the structure and was lobotomized for his actions; presumably trying to aid the people inside in their escape. This is aided by the actions done by someone in Zero. If he made it, we'll probably never know--but more than likely he didn't succeed.

Our songs will all be silenced, but what of it? Go on singing. -- Orson Welles

There is actually a very elegant and profound meaning behind this film:

The cube is a metaphor for life.

There is nothing more to it. Some people prefer a complex, literal interpretation, but I don't think that is helpful.

People were placed in a cube (the world). They do not know the purpose of this cube (meaning of life). They assume someone had to have created the cube (a higher power with a divine plan). They debate their existence in this cube (theology and philosophy). They pass through numerous rooms filled with obstacles, gradually becoming more attuned to how the cube operates and devising plans to survive in their environment (science and technology). They must all cooperate to maintain order, even despite their differences, or run the risk of anarchy and eventual self-annihilation (society and politics).

And, of course, the very last scene where Kazan walks into the light at the end of the tunnel is a metaphor for heaven and the afterlife.

Cubes don't have points. Cubes have sides.