Baal HaSulam, The Study of the Ten Sefirot, Part 3, Chapter 1, Item 6: Thus the Masach (screen) that reaches the upper as a result of the incorporation of the lower in it is called a window, since there are no Dinim in it, but only a reason for illumination, like a window.
The lower enters the upper and awakens it and demands to receive the Light from the uppermost, thus creating a window in the upper. I demand the upper to convey the Light for me, and it is as if I make a hole in it that way.
The upper level works like an electric amplifier with a great resistance at the entrance. It is very important that I don’t affect the amplifier and don’t bring myself into it but only operate it by my action. I don’t connect my system to its system, but only give my signal to its signal.
Thus, the amplifier should have a very high impedance at the entrance. In the past, amplifiers were made of diode lamps with strong resistance and not with transistors. Then, you could be sure that you are not affecting the system in any way or making any changes in the system, except for operating it.
This is how the spiritual levels are made. However, we must overcome this great resistance. Our work is to overcome the desire to receive this way in order to annul the resistance and to insert only my bestowal into it. Technology allows us to do that by connecting semi-conductors. In the spiritual work, I need the Light of Hassadim in order to annul the resistance.
The Light of Hassadim symbolizes my yearning for pure bestowal without connecting the whole system to the upper system. I only want to insert my net bestowal into the upper, and so I immediately annul all the limits and make a “window” in it through which I reach the uppermost.
From the 3rd part of the Daily Kabbalah Lesson 1/20/14, “The Study of the Ten Sefirot”