Bhagavad Gita Chapter 13, Text 13

Bg 13.13

jneyam yat tat pravaksyami
yaj jnatvamrtam asnute
anadi mat-param brahma
na sat tan nasad ucyate

Word for word: 
jneyam — the knowable; yat — which; tat — that; pravaksyami — I shall now explain; yat — which; jnatva — knowing; amrtam — nectar; asnute — one tastes; anadi — beginningless; mat-param — subordinate to Me; brahma — spirit; na — neither; sat — cause; tat — that; na — nor; asat — effect; ucyate — is said to be.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
I shall now explain the knowable, knowing which you will taste the eternal. Brahman, the spirit, beginningless and subordinate to Me, lies beyond the cause and effect of this material world.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Lord has explained the field of activities and the knower of the field. He has also explained the process of knowing the knower of the field of activities. Now He begins to explain the knowable, first the soul and then the Supersoul. By knowledge of the knower, both the soul and the Supersoul, one can relish the nectar of life. As explained in the Second Chapter, the living entity is eternal. This is also confirmed here. There is no specific date at which the jiva was born. Nor can anyone trace out the history of the jivatma’s manifestation from the Supreme Lord. Therefore it is beginningless. The Vedic literature confirms this: na jayate mriyate va vipascit (Katha Upanisad 1.2.18). The knower of the body is never born and never dies, and he is full of knowledge.

The Supreme Lord as the Supersoul is also stated in the Vedic literature (Svetasvatara Upanisad 6.16) to be pradhana-ksetrajna-patir gunesah, the chief knower of the body and the master of the three modes of material nature. In the smrti it is said, dasa-bhuto harer eva nanyasvaiva kadacana. The living entities are eternally in the service of the Supreme Lord. This is also confirmed by Lord Caitanya in His teachings. Therefore the description of Brahman mentioned in this verse is in relation to the individual soul, and when the word Brahman is applied to the living entity, it is to be understood that he is vijnana-brahma as opposed to ananda-brahma. Ananda-brahma is the Supreme Brahman Personality of Godhead.