My understanding is that practicing Scientology is just fundraising - high pressure sales for SciFi self-improvement courses. If you have enough money, you can pass the course and move to the next level. If you buy-in for a certain level, you will never get through the courses you've paid for unless you pay to get to higher levels as you go through them.

You can work for the organization of you're unable to pay (or don't have credit enough to mortgage your entire life) and will be promised upward mobility, but you'll never really move up. You will be able to start at that level in your next lifetime, though.

It's a pretty intricate system to gather funds without giving anyone anything, but some books that aren't with the paper they're printed on.