Of Rays and Impressions - The Kav and the Reshima (Unit 3 Unifications Ch. 9, Ch. 11 in DM)

But in fact, though the Ten Sefirot are a product of the contraction, the Cleared Away Space. Nevertheless the Infinite Light that comes into them is from beyond the Contraction and this is the "Ray" from the Infinite Light, and this Remaining Impression, Imprint, and Ray are discussed elsewhere...

There is a discussion between the kabbalists for several generations about the nature of the contraction known as the Cleared Away Space. This was also a point of contention between the Chasidim and the Misnagdim. It concerns whether the Cleared Away Space [which hides G-d's existence from the creations] is an objective reality or not. According to the Gaon of Vilna, it is an objective reality, a real vacuum or veil. 

But according to the Chasidim it is only a matter of perspective, a one-way mirror. There's a likeness to this idea. Two people are talking and the one who is speaking pauses speaking for a moment. From the listener's perspective, the conversation halted completely. But for the speaker the pause is part of a natural flow. From the speaker's perspective the conversation did not stop at all.

There is a Ray of Light that was drawn into the Cleared Away Space and it is a continuation from the previous  uncontracted Illumination. It gives life to all the Creation. The Cleared Away Space also contains an Imprint of the previous existence [which is the root of Vessels or Sefirot, that receive the Light]. What is this Imprint? Every space is in context to the reality that was cleared away to create the space. It isn't completely empty. It contains some impression from the previous stage of existence. For instance, someone once said that Modern European culture is the Cleared Away Space from Christianity, and I say Modern Israeli culture is the Cleared Away Space from Judaism...

These two objects, the Ray and the Imprint make up the Lights and Vessels, the Spirit and Matter of the World. The Tzemach Tzedek goes on to explain that the aspect of the Ray that is drawn into the Unification of different vessels, is an aspect of the original light that preceded the Cleared Away Space.

(The text in italics are the words of Derech Mitzvosecha by the third Lubavitcher Rebbe, the Tzemach Tzedek. The bolded words are Rabbi Adin Steinsaltz's commentary as heard on his shiurim on hashefa.co.il. The rest is my commentary. All rights reserved to Rabbi Steinsaltz. Pictures courtesy of Moshe Schlass.)