OK, here are my two cents. Not sure if this will help but this is how I think about this in contemporary terms:
Let’s say you have never experienced snow before but you are very interested in it and have read and studied it for years. How does that conceptual knowledge compare to the experiential wisdom of finding yourself out in a field of snow for even a few minutes? You would probably reflect on your study of snow and think “OK, this is what they were talking about, this is what they meant”.
This is what I think AN4.77 is about: that there is a big difference between conceptual understanding and experiential understanding (knowledge vs wisdom).
And this distinction between conceptual and experiential also applies to two modes of our mind often thought of as head vs heart or cognitive vs feeling. The cognitive or thinking mind is dominant in pretty much all of us over about 13 years of age. Nevertheless, we are constantly switching back and forth between these two modes without being aware of it. We make this shift whenever we need to really tune into our senses - a faint sound, a distant sight, or think of an artist like a painter or sculptor, a wood worker or basket weaver - there is a kind of flow that they can get into where the thinking mind is stilled and they are absorbed in there work.
Jhana is not unthinkable but rather non-verbal from the second one onward. And even in the first it is not thinkable in the sense of everyday discursive thinking and chatter. But one is quite lucid so it’s easy to reflect on it afterwards. But if you have that experience and then describe your experience to me (and I have not had it) then for me it is conceptual. But importantly, it gives me an idea of what the experience is like similar to how your study of snow led you to recognize that it was snow when you had the actual experience.
The following two quotes describe making the shift between thinking to feeling in terms of left brain and right brain modes:
“In order to gain access to the right brain [feeling mind], it is necessary to present the left brain [thinking mind] with a task that it will turn down.”
“In other words, it is no use going up against the strong, verbal, domineering left brain to try to keep it out of a task. It can be tricked, however, into not wanting to do the task, and, once tricked, it tends to “fade out”, and will stay out, ending its interfering and usurping. As a side benefit, this cognitive shift to a different-from-usual mode of thinking results in a marvelous state of being, a highly focused, singularly attentive, deeply engaging, wordless, timeless, productive, and mentally restorative state”. - Source Drawing on the Right Side of the Brain pg: XXV
In my view, the first jhana is acting like a bridge between the thinking mind and the feeling mind. It repeatedly gives the thinking mind a task that only the feeling mind can handle (“pointing the mind”) which causes a shift to the feeling mind. Then we attend to, nurture, savor the resultant feeling as long as possible (“keeping it connected”) until it starts to fade and then “point the mind” once again to sustain the focus. The first jhana has completed its task when the mind is able to stabilize in “feeling mode”, and the thinking mind drops out of the experience.
The purpose of the first jhana is then to clear away the mental chatter so as to become aware of what is going on beneath all that noise.