Now, as explained above, there is actual speech and there is speech of thought. Speech is known as the open Mem (מ), because of the fact that it is open and revealing. In contrast, thought is known as the closed Mem (ם), for it is hidden and concealed. (As mentioned earlier speech is called “The Revealed World” whereas thought is called “The Concealed World”.)
Now, in the thought of Binah itself, there is also an open Mem (מ) and a closed Mem (ם). These are called the “Open Saying” and the “Closed Saying”. In order to understand the difference between these two in thought, we must understand that which is explained in Kaballah, that the encompassing lights of Binah are square. If a person is in the middle of a square room, part of the ceiling is directly above him and close to him, and part of it is across the room and far from him. Likewise, the encompassing lights of Binah (Understanding) are square. In other words, the part of the concept under analysis which he understands is “directly above him”. The part of the concept which he does not yet understand is “across the room” and far from him. This is like the shape of the closed Mem (ם), which is a square. Therefore, within thought itself, the closed Mem (ם) refers to the encompassing lights, as explained.
(The encompassing lights of Binah are different than other encompassing lights, which are round. Something which is round is equidistant on all sides. This is not the case in regard to the encompassing light of Binah which is not equidistant. This is because, when it comes to understanding, there always is a part he understands, and a part which is concealed from him, which he has yet to understand.)
In contrast, the open Mem (ם) refers to how the ray from the encompassing light is revealed in divisions and combinations of letters of thought.