One can understand this only if one understands that it can not be understood, and one is not able to understand this if one thinks it can be understood.
Yes, this is the ultimate Truth. But this is not where the story ends -- that is where it really begins! Before we can know anything, before we can define the concept of "truth", before we can have the freedom to, finally, get on the trail of discovery, we had to find the trailhead.
That same concept was proposed many times later under different names. Here are a few examples by Western philosophy:
- All of Immanuel Kant's "Critique of the Pure Reason"
- Socrates' famous quote, "The only true wisdom is in knowing that you know nothing"
- The proposal by René Descartes, known henceforth as "Cartesian doubt", echoed by
- Søren Kierkegaard's "leap of faith"
... just from the top of my head. Put in plain English, it means that your own existence, while self-evident, is the only truth you will ever know.1
Call it the Ultimate Truth, 'cause you won't get any further by staying rational and relying on pure reason alone, as the title of "Critique..." suggests.
And that's how we "understand that it can not be understood".
Bottom line, no one was particularly impressed with the pure reason's performance, because, ultimate or not, ignorance a lousy final destination for purely practical reasons. Which is what the second "Critique(?)..." was about --because in the end, "To Be is to Do",3 and knowing nothing isn't much to go by, is it?
So what for a rational person to do in this situation? Well, that's what faith is for -- when there is no reason, one must have faith.
Yes, we are ditching rationality, but we are doing it for rational reasons, and, otherwise, we stay rational about it -- about being irrational.
"One can understand this only if one understands that it can not be understood" -- it's no wordplay, and, hopefully, you will see it too.
So staying rational is not an option -- on the one hand. On the other hand, abandoning rationality for good is not an option either (I mean being rational, acting rationally -- that WAS the whole point, isn't it?.. to understand, to know the truth -- so we can see clearly and, maybe, even know what in the world we are doing?).
That makes it about finding the right balance -- rather than replacing rationality with blind faith, we must make it a leap. Just this one time, we are going to act on faith and simply assume that we, well, can be rational.4 The tenets of our faith, if true, must allow for a strictly rational system of beliefs from that point onward. I'm only aware of one such set -- these days we call it "the objective reality", but in pre-civilization cultures, we referred to it as "God".
Specifically, the "objective" part means:
a) we all share the same, one and only reality,
b) we ourselves are a part of it,
c) we perceive it in very much the same way, and
d) it is explainable
The first three conditions allow for a valid definition of truth -- and it is only valid if it also defines what is not true.5 It also must make the truly objective and universal: what is true for one must be true for everyone else (we can have differences in opinions, even tho it doesn't reflect well on us).
The explainable part means that things never happen at random -- tho "not at random" does not necessarily mean they happen for a reason. Rather, it means we can always, at least in theory, trace their cause to some past events. In fact, our brains are hard-wired with that capacity, the capacity to understand the logic behind events.
The Koine Greek word for that faculty was "lógos":
‟Through it7 all things were made; without it, nothing was made that has been made.
-- John 1:3
And if only we had the will to use it! But, for many thousands of years now, we just don't.
‟The lógos holds always, but humans,
always time and again, prove unable to ever understand it, both before hearing it and when they have first heard it.
-- Heraclitus, circa 450 BC
1 ... slightly complicated by the fact that most people simply do not deal in knowledge (so if my "plain" English isn't really... well, you are not alone)
2 looks like an ivory tower... otherwise totally unintelligible, and so even more imposing
3 ... and I don't even know whose quote is that anymore (though I'm pretty sure it's Socrates')
4 BTW, rational means explainable ;) For example, a belief is rational if you can explain why it is true.
5 Because we need to know what is not possible in order to know our options, to have a choice, and, therefore, freedom.
7 Koine Greek "lógos", Aramaic "miltha", or Sanskrit "ātman" refer to the same concept, but no modern language has a word for it. Latin was already too modern, so in the Latin translation of Gospels "lógos" simply turned into "verbum" ("the word"). Probably meant as a placeholder, until they figured out a proper translation, but (in the rush?) things slipped through the cracks, as they often do.