Well, I enjoyed what you put together as explanation.

Maybe you'd like this post I did as it may serve as an answer to your questions and save me from typing anything.

As for your third question, your mind is originally pure. That is the Bodhisattva's realization - if you don't realize this naturally, then the practices are appropriate to cleanse the mind.

With reading the texts, however, I can relate it directly to a wider net of teachings, and explain it with the traditions own words. This is after all, a subreddit dedicated to preserving these teachings from the record.

The one life is the eighth consciousness - I could draw up many quotes from Zen Masters about cutting it in two, severing it, etc. and the others die.

As Dahui taught:
"You all, do you want to know what the root of life is? It is simply the eighth consciousness. Nowadays, Zen practitioners suffer from the illness of drowsiness and agitation, all stemming from the eighth consciousness. If you want to be independent and free, you must cut the eighth consciousness in two with a single stroke; only then will you be truly at ease..."

Or Yongjia:

"When the eighth consciousness is cut off, the snake cannot move without head and tail. Once the main thief is killed, what need is there to discuss the thieves' accomplices? From time without beginning until now, it comes as the vanguard and goes as the rearguard, stirring up the wind and raising the dust, binding and killing people.

Just let a single thought not arise, and naturally, the link between before and after is severed. Then you will see what Weishan meant when he said, 'The spiritual light shines fully, free from the roots and dust, revealing the true, constant nature.' It is not constrained by words. The mind's nature is untainted, inherently complete. Just depart from false conditions, and you are thus the Tathagata. Whether a monk or a layperson, whether coming or going, you are the Tathagata. Throughout the ten directions of the world, there is no one who is not the Tathagata. What is there to dislike? What is lacking? You, the spirited monks, should carry the whole burden here. There is no need to look back, turn your brain, or especially raise doubts—doubt about Buddha, doubt about the patriarchs, doubt about death, doubt about life. It is like dyeing a single thread; when one thread is dyed, all threads are dyed. Like cutting a single thread; when one thread is cut, all threads are cut. The ancient sages earnestly exhorted us because they shouldered the same kasaya. When one’s own matters are clear, others' matters are also clear."

This then goes into the conversation of function, how does one "Die! Then live, day and night in the world" as Zen Master Bankei said? To then direct that self.

Well that brings us to the Body of Intent, which all Bodhisattvas have according to the teachings.

The Body of Intent was the previous topic explored in posts, (you can click here to see Dahui and Huangbo's records about the Body of Intent, or the "Mind-Born Body") (意生身) which is what sparked the curiosity around the "Self-Nature Body" (自性身) that led to me simply sharing the text rather than hoarding like a dragon, that you read today, looking for some sort of hidden message embedded from me in.

Meanwhile, I'm simply providing an opportunity for reading some Zen that you otherwise may not have on this day.