Chapter Fourteen: (i) Understanding this notion of an “Existence which is a Non- Existence, Yet Remains as an Existence”: In the service to G-d we find: (a) The nature of a man who loves, and get close to, Torah, however, they are embarrassed from their surroundings, being that the existence of the others disturb him. (b) However, when he is in a dimension of Truth, that everything exists only for the Will of G-d, then his service is one of truth, and existence of others doesn't interfere with his service. Thus, we find that there are auspicious moments (Rosh Hashanah, Yom Kippur, etc.)
when he experience a spiritual elevation, and nothing else exists to disturb him. (ii) These two dimensions: (a) When he is effected by the existence of others, who in truth, are a non-existence that are in existence, then he is in the Inferior Knowledge, the Lower Self-Negation of only his Ego, which is the Faith of the Finite Permeating Linear Light. (b) When he stands higher, in a dimension of Truth, that nothing else has an existence before the Infinite One, blessed be He, then he is in the Superior Knowledge, the Higher Self-Negation of even his Existence, which is the Faith of the Infinite Encompassing Circular Light.
--The Rebbe will explain this in the concept of how those who had self-sacrifice in Russia, and yet lost their self sacrifice when they arrived in America.