A few thoughts
EA teaches that it can take hundreds or thousands of lifetimes for a soul to evolve from even one substage to the next.
I don't recall ever hearing anything in EA that said it can take hundreds or thousands of lifetimes to evolve through a single substage. It does say it can take a really long time, longer than we like to think.
I recall reading Yogandanda saying that it is the natural evolutionary condition of nature that a human being will reach what some call enlightenment, naturally, over the course of a million years, without making any special effort at all. Its part of how human life was created. Yogananda taught that the Kriya yoga techniques that he taught (and there would be other techniques taught on other paths also, of course) are intended to speed up that natural process. In essence, that God had included as part of creation (natural law) ways that those who so desired
(i.e. choose, voluntary) could accelerate the pace of the natural evolutionary process. These ways are built in, thus they are also part of natural law.
It is taught in the Tibetan lineage that Milarepa achieved Vajradhara, which I understand to be the equivalent of third stage spiritual (though I may be completely wrong here) in 1 lifetime.
Therefore I was wondering what such a notion of "enlightenment in 1 lifetime" could mean.
I'm not familiar with the details of this. What I'd like to suggest is, the story as you presented it does not indicate what Milarepa's background was. He did not go from a protozoa to an enlightened human spiritual master in a single life, that I will guarantee you.
Most people who finally "achieve enlightenment" in some life have a desire nature firmly developed that has been concentrately seeking that liberation for a series of lives, potentially a long series of lives. This creates an inner psychological nature, a character (the nature of the desire nature), that is pre-wired in any given birth to even more of that. In essence a process of elimination of separating desires has been occurring for a long time. That final release from the wheel has to occur in some
life - when there are witnesses to someone breaking free, they see the before and after effects on that person. They don't see how many lives it took that person to get to the life in which they were finally liberated.
It is clear to me that Milarepa had a very strong desire for complete liberation. I understand that desire is the bottom line determinant for the degree of evolution that any soul can experience...
... therefore another question comes up for me:
1. CAN a soul evolve through many stages in 1 lifetime? I intuit that most souls come into a particular life with a pre-established intention to only go "so far" (and thus picked all the circumstances ahead of time that would be conducive to it's evolutionary intentions). However, does the possibility exist, WITHIN an actual lifetime, for a soul to cultivate the desire to "go further" and actually achieve that?
To me one of the key the limiting factors in how far a soul can go in a single life is how much the human can bear to take on in a single life. When we look at charts with 7, 8, 9 planets aspecting Pluto, and/or 4, 5, 6 retrograde planets, typically these people have had very intense lives. Lives most humans would say they would never wish on another, or want for themselves. Why? Why would a soul take on a life like that? Because it accelerates the exhaustion of separating desires. They are literally ripped away, ready or not, over and over. Emotionally and humanly, many of these experiences are painful and difficult to integrate. They are taken on as part of accelerating the evolutionary process.
PTSD boils down to, more emotional voltage flowing down the nervous system wires than the wires are designed to handle. The wires literally burn or melt, creating permanent changes in the brain. It takes a tremendous amount of determination and focused desire to take all of that on, and there are limits to how much the circuits can handle.
You wrote the other day of continuing to meditate vs talking to a woman you would have liked to talk to. How many people are ready to make choices like that 24 hours a day, seven days a week, every single year, every single time? Without repressing the desires to do the other things (separating desires)? Repressing or "transcending" naturally occurring desires (and separating desires are naturally occurring since they also originate in the Soul) is not the same thing as exhausting them.
It would take an incredibly intense lifetime to deal with all of that in a single lifetime, and I kind of doubt there are any humans who could handle it. Most of us need to attend to our human needs and wants at the same time we try to energize our "return to source" desires. It becomes too painful, extreme, alienating, or alone to simply pursue merging with this inner divinity 24 hours a day every day.
People seem to feel that coming into a state of what we call enlightenment is some great release from all the pain disappointment and discomfort in human life. When you look at the actual lives of the people we consider enlightened, you notice one pretty commonly shared factor, that most of them had very difficult lives with tremendous personal discomfort. They are still in human bodies, the body still has human tendencies and needs. And yet, they are continually called on to surrender one step further, to become ever purer vehicles for God/dess work, to let go of their personal needs and fears and desires, to give give give (as inwardly directed), expecting nothing in return. Almost no other people have the slightest idea of their inner reality, which is completely different than the inner reality of the vast majority of the human race. Its between them and God, and God's helpers who they work with. They are continually misunderstood and projected on. And they have to learn to bear all of this with dignity and a kind heart with tenderness, and a sense of humor. They are often given assignments that are not at all fun. It is a tall order. That is precisely why for the vast majority of the human species it does take a long time to get there. We are unwilling or unable to do enough of what is required to go all the way in a given life. Doing that requires changing the inner desire nature within the Soul into one that is deeply dedicated above all else to doing just that, 24 hours a day. Very few of us are anywhere near that place. And for most it requires a series of lives to change that inner desire nature.
Another thing you might ask yourself Ari, is "What's the rush?". Where is anyone going that they need to be in this great hurry to get there, vs accepting the natural limits inherent in the human form, that for 99.99% of us, it is a drawn out process. I do know that the American tendency is to want to be the fastest, the first, the best, the biggest. You have to make sure that none of that cultural conditioning is the motivator of wanting to speed that whole process into a single lifetime. That is not going to be possible until the only
remaining underlying desire is total love of God, and willingness to sacrifice anything and everything as necessary, at any time, to carry out God's intentions, with no underlying desire to get anything back for doing so other than knowing you have done the right thing. While observing every day that people who do the "wrong thing", that is, advance themselves at the expense of others, or seek to do the right thing while wanting to reap the reward or credit for doing so, seem to be getting the recognition, the material benefits, while you often seem alone, not recognized, under appreciated. How many people would be able to go through all of that in a single life?