It's a common motif in spiritual systems. Compare with archangel Gabriel ('the intellect') accompanying Muhammad on his mystical ascension (Miraj) stopping at the boundary of the 'central tree' and claiming he could go no further as it would burn its wings. (In a continuing series of cosmic winks please note that this ascension is called 'The Ladder' in Arabic and we also have a tree ...)
This is worth reading. Nagarjuna had similar ideas, going beyond the metaphor of raft.
1] Nāgārjuna, Nietzsche, and Rorty’s Strange Looping Trick
Philosophers have lots of tools and tricks up their sleeves. They, of course, can use formal argumentation, they can employ all sorts of thought experiments to elicit various intuitions, they can lay out examples, dilemmas, dialectics, and do a whole host of other things. But I want to talk about one particular trick that only a select few philosophers have employed. This trick involves wrapping everything up in a philosophical system only to have that system knock itself down by its own internal means, and doing all in order to produce some sort of anti-philosophical result. I’ve come to call this the “looping” trick, and it’s one of the most philosophically curious things that I’ve ever stumbled upon.
https://en.wikipedia.org/wiki/Sidrat_al-Muntaha