....On Simchas Torah 5738, the Doctors ran many tests on the Rebbe, and they had to draw blood a number of times. One of these times the Rebbe asked one of the physicians, what it was that withdrew the blood? Was it the needle which broke the skin, that withdrew the blood or was it the vacuum which is created in the syringe that extracted the blood? The doctor answered that it was the vacuum. I express interest in this, the Rebbe said, because someone came to me on yechidus and said that it was a waste to bother to influence him in matters of Torah and mitzvos, because he is empty and vacuous, bereft of any substance... To this I responded to him - the Rebbe continued - that the opposite is true; the emptiness and vacuum draw down deeper powers of one's soul, they bring to a greater need to fill that void...the vacuum becomes a vessel to intensify and bring down holiness and be filled by it.
The Rebbe later said that this is his “sermon” for Yom Tov, and he asked that this be elaborated in detail at the Simchas Torah farbrengen. The vacuum created by the vacant seat [referring to his place at the farbrengens], should draw down greater simcha joy...
(Simchas Torah 5738)