You need to "think like a brain-washed & severely over-indoctrinated Scientologist" to grasp the simple "logic" involved.
In Hubbard's view, as stated clearly in MANY policies and books, and thus in the mind of every card-carrying Church lemming, ONLY LRH Tech supplies the tools to FREE THETANS. That is a Scientology stable datum - part of the fanatical belief system created in the mind of any person staying involved with the subject for too long.
So, when one accepts this "fact" (it's not really a fact at all, but is accepted as a "fact" by the Church looney follower), that ONLY Scientology provides the "road to complete spiritual freedom, well then "logically", within the Scientology framework of BELIEFS, if you leave Scientology, get declared, and become banned from all upper levels, you thus are cutting yourself off from gains FOREVER! For "eternity". (ref:
From Clear to Eternity - LRH ED, "RJ" something or another)
Yeah, I know it is dumb. But, this is what these dummies accept, believe and forward to others as "truth".
There is a bit more to it though. If you "leave", you then get declared as an SP. The expulsion and declare follow naturally, again within the framework of Scientology policy idiocy. If you are declared, you are forbidden from getting any Scientology services, and since, again within the framework of their thinking, since ONLY Scientology possesses the ONLY workable path to spiritual enlightenment on planet Earth (more stupid assertions and assumptions), well OF COURSE, you are throwing away your priceless eternity.
Hubbard yaps about this endlessly. This belief, that ONLY Scientology holds the key to your eternal salvation, is KEY to continuing the scam on any true believer. That YOUR endless eternal future depends on what YOU DO with Scientology by getting yourself up the Bridge, right now (ref: KSW). If you don't get up the Bridge, either due to laziness or getting yourself denied the Bridge (by leaving), well then you are "throwing away your eternity".
I cover all of this in the essay referenced below.
To understand a Muslim fanatic, you must learn to think like one by understanding what the nut-job BELIEVES. The same is exactly true when trying to understand what a fanatical devoted Scientologist thinks, believes and DOES.
Oh, and if you try to do the Bridge NEXT lifetime, the theory is that it would come up in auditing that you were declared last lifetime, and that you would either have to do A to E, or remain declared and cut off from the Bridge and your "wonderful sparkling eternity as an OT". Gag me with a spoon . . . .
If each of the assumptions are true, then it "makes sense" (follows logically) that you would be throwing away your eternity. The problem, of course, is that the assumptions, claims and assertions of Hubbard and Scientology are NOT TRUE!
You can only understand the behavior of any person once you grasp the person's fundamental beliefs about reality. And sadly, what any person accepts as true and believes often has very little to do with any observable verifiable "fact". This is especially true with "religions".