It was already explained at length in a special tract (namely Kuntres HaHispaalus - A Tract on Excitement) about the specific types of excitation of the mind, heart and thought that are born from hisbonenus-meditation, according to the five levels of the soul - NiRaNCha"Y (Nefesh, Ruach, Neshamah, Chayah, Yechidah).
Now that the importance of hisbonenus has been explained, we have to explain the nature of hisbonenus-meditation itself (as opposed to its affect on a person that was already addressed in A Tract on Excitement)- what it is essentially and about what one should meditate.
The Mitler Rebbe will now define hisbonenus and then proceed to explain the mechanics of thought in general, demonstrating how hisbonenus interacts with the three faculties of the mind Chochmah (wisdom), Binah (understanding) and Daas (knowledge). In doing so he will describe how each of these faculties include three dimensions a length, width and depth and the meaning of these dimensions. In the words of the Mitler Rebbe:
The essence of hisbonenus is to gaze strongly into the depth of a concept, focusing on it for a long time, until one understands it clearly with all of its minute details. This process is the inner aspect of the faculty of Binah and is what is called in the Talmud "Eeyun" -in depth repetitive study or analysis, as opposed to the surface level mode of study called "Geersah," both of which will be explained in the following. As it says in tractate Sukkah there is one mode of study that is a ‘Geersah’- surface level study and there is another mode of study, which is an ‘Eeyun’- in-depth mode of study."
The definition of ‘Geersah’ is to only understand something according to ones first glance. Meaning that one rushes quickly on to the next subject without any restraint or pausing at all to examine the subject closely, as is known. This being analogous to one who sees something without thinking at all about the quality and nature of what he sees, with all of its inner and outer aspects, but rather, he looks at it merely in a passing manner. So that inevitably, in the course of time he will surely forget about it completely. Similarly, even immediately after seeing it, he will only be able to described what he saw in general terms. This is because he saw it only with a passing of the eye, not absorbing what he was seeing at all.
This dilemma is often found amongst witnesses, for often in the suddenness of a crime people do not properly take in the details of what they are seeing and later have trouble describing the event clearly to the authorities. So that valuable details such as what the criminal looked like, how he got away, and even details of the actual crime that occurred can get skewed. Only a few general facts tend to stick out. Like, for example, a gunshot, screams, an explosion, a collisions of cars, etc. However, when it comes to the valuable details often there are contradictory reports, as people’s imaginations fill in the details they missed, (perhaps in their embarrassment at their lack of recollection).
So too with the passing of the minds eye over a given explanation, understanding it only according to one's ‘first glance,’ without pausing to examine the idea well. So that the result of such a study is that one does not know the idea completely at all. This is called Geersa study.