I have a question which, although it may not be very relevant at this stage anyway, has been puzzling me:
If the ego is an element of the Astral body, what keeps the soul bound to the causal body, once the astral body has been shed?
I agree: The answer to this question is not vital for most of us yet — and perhaps it never will be, since it really doesn’t help us get out of ego. But I’ll offer some thoughts anyway.
Although the ego is indeed an element of the astral body, it is also an element of the causal body, although in a slightly different way. Therein lies the answer to your question. (See Autobiography of a Yogi, chapter 43 — a mind-bender of a chapter.)
Here’s a simple way to think of it: The causal body contains a “blueprint” for the astral and physical bodies. On the physical plane, we think of blueprints as inert pieces of paper, but like everything in creation, that causal blueprint is alive with God’s consciousness. It is a living blueprint. Subtle though it is (being “mere” thoughts), it nevertheless holds that essential egoic awareness: “I am.” As "condensation of vibratory forces" (as Sri Yukteswar put it) induces that causal “I am” awareness to take form in the astral, then physical planes, it becomes increasingly limited. But even at the causal level, there is some limitation in that “I am” thought.
In fact, God too has the “I am” awareness. But one could call that divine ego: the consciousness of existence, without being limited in any way whatsoever. God’s “I am” is “I am everything,” whereas common human awareness is “I am the body” or “I am the personality.” Big difference. And even the causal “I am,” though far less limited than common human awareness, still falls short of “I am everything.”
So the bad news is that, even once we shed the astral body for good — done with all astral and physical karma, residents of the causal realm only, never again having to reincarnate in the astral world — we’ll still have egos, so we’ll still not be free in God. The good news, however, is that Paramhansa Yogananda assures us that, through the science of yoga, we can jump directly from physical incarnation — right past all that causal stuff — to final liberation in God. Let’s do it!