13.23 He who is the upadrasta, Witness, who while staying nearby does not Himself become involved: As when the priests and the performer of a sacrifice remain engaged in duties connected with the sacrifice, there is another (called Brahma) remaining nearby who is unengaged, is versed in the science of sacrifices and witnesses the merit or demerit of the activities of the priest and the performer of the sacrifice, similarly, He who is not engaged in the activities of and is different from the body and organs, who has characteristics other than theirs, and is the proximate (upa) observer (drasta) of the body and organs engaged in their duties, is the upa-drasta. 
Or: The observers are the body, eyes, mind, intellect and the soul. Of them the body is the external observer. Proceeding inwards from that (body), the Self is the inmost as also the proximate observer, compared with which there is no other higher and inner observer. The Self, because of being the most proximate observer, is the upadrasta. Or, It is the upadrasta since, like the non-looker of a sarifice, It witness everything.
And He is the anu-manta, Permitter: Anumananam, approval, means satisfaction with those performers (viz body and organs) as also their perfomances. The agent of that (approval) is the anumanta. Or, He is the anumanta since, even though Himself not engaged in the activities of the body and organs, He appears to be favourably disposed towards and engaged in them. Or, He is the anumanta because, when the body and organs are engaged in their own functions, He remains as a witness and never dissuades them.
It is the bharta, Sustainer: Bharanam means the continuance in their own state of the body, organs, mind and intellect, which reflect consciousness and have become aggregated owing to the need of serving the purpose [Viz enjoyment, or Liberation.-Tr.] of some other entity, viz the conscious Self. And that (continuance) is verily due to the consciousness that is the Self. In this sense the Self is said to be the Sustainer.
It is the bhokta, Experiencer: As heat is by fire, similarly, the experiences of the intellect-in the form of happiness, sorrow and delusion in relation to all objects-, when born as though permeated by the consciousness that is the Self, are manifested differently by the Self which is of the nature of eternal Consciousness. In this sense the Self is said to be the Experiencer.
He is maheswarah, the great God, because, as the Self of all and independent, He is the great Ruler.
He is paramatma, the transcendental Self, because He is the Self which has the characteristics of being the supreme Witness etc. of (all) those-beginning from the body and ending with the intellect-which are imagined through ignorance to be the indwelling Self. He is api ca, also; uktah, spoken of, referred to, in the Upanisads; iti, as, with the words; 'He is the indwelling One, the paramatma, the transcendental Self.' [Ast reads atah in place of antah. So the translation of the sentence will be: Therefore He is also referred to as the transcendental Self in the Upanisads.-Tr.] Where is He? The parah, suprem; purusah, Person, who is higher than the Unmanifest and who will be spoken of in, 'But different is the supreme Person who is spoken of as the transcendental Self' (15.17); is asmin, in this; dehe, body.
What has been presented in, '৷৷.also understand Me to be the Knower of the field' (2), has been explained and conclude.