pṛthaktvena tu yaj jñānaḿ
nānā-bhāvān pṛthag-vidhān
vetti sarveṣu bhūteṣu
taj jñānaḿ viddhi rājasam

Translation of Bhagavad Gita 18.21

That knowledge by which one sees that in every different body there is a different type of living entity you should understand to be in the mode of passion.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

The concept that the material body is the living entity and that with the destruction of the body the consciousness is also destroyed is called knowledge in the mode of passion. According to that knowledge, bodies differ from one another because of the development of different types of consciousness, otherwise there is no separate soul which manifests consciousness. The body is itself the soul, and there is no separate soul beyond the body. According to such knowledge, consciousness is temporary. Or else there are no individual souls, but there is an all-pervading soul, which is full of knowledge, and this body is a manifestation of temporary ignorance. Or beyond this body there is no special individual or supreme soul. All such conceptions are considered products of the mode of passion.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

This verse speaks of rajasic knowledge. That knowledge which one sees the soul as different in each body that it accepts, accepting the asuric idea that the soul perishes with the body, with a different soul in every body that arises; that knowledge by which one knows various opinions arising from such asuric scriptures, such as “the soul is the shelter of happiness and distress, the soul is not the shelter of happiness and distress, the soul is unconscious, the soul is conscious, the soul is all pervasive , the soul is atomic, the souls are many, the soul is one” is known as rajasic knowledge.

Commentary by Sri Ramanuja of Sri Sampradaya:

18.21 Whatever knowledge perceives in Brahmana etc., at the time of work, the entity known as the Atman as of diverse nature because the bodies of those beings are tall or fair and are fit to attain the fruits of work — know that knowledge to be Rajasika. The point is this: It is not a condemnation of the plurality of Atman. The Atman, though distinct, is uniform everywhere. The bodily attributes do not affect it. The knowledge lacking this understanding is stigmatised as Rajasa.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Now the nature of knowledge in raja guna or mode of passion is explained by Lord Krishna. The knowledge where one imagines all jivas or embodied beings as distinct, possessing different atmas or souls diversely conditioned by pleasure and happiness and pain and suffering is situated in raja guna.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

That knowledge which is contrary to the Vedic scriptures and the antithesis to the omnipotent absolute authority of the Supreme Lord Krishna is known to be situated in raja guna the mode of passion. The words nana-bhavan mean multiplicity of natures. Those who are oblivious that the Supreme Lord is the one underlying reality pervading all creation, simultaneously existing within the etheric heart of every jiva or embodied being in existence; are situated in raja guna.

Now begins the summation.

If one is unaware of the Supreme Lord Krishna’s unparalleled position as the absolute sovereign ruler of all existence, or is bewildered about His indomitable, paramount position or thinks that any other god can manifest creation or are influenced by inferior concepts, doctrines and philosophies concerning creation, the jiva and the Supreme Lord; such erroneous and fallacious thinking devoid of a connection to reality impels one to obstinately and belligerently try to justify and validate their illusory belief systems. Such fools of miniscule knowledge and misguided intelligence are unable to mount a rational argument supporting their viewpoint and odiously cling to their bogus suppositions and faulty claims.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

That knowledge which has been characterised with raja guna the mode of passion cognises the manifold existence of the jiva or embodied being as related to physical bodies, seeing division in difference of forms, species, genre, etc. Establishing criteria based on bodily conception and oblivious to the true reality of the omnipresent atma or immortal soul such jivas are undeniably rooted in raja guna. The particle tu meaning however indicates that raja guna inferior to sattva guna.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

18.21 Tu, but; viddhi, know; tat, that; jnanam, knowledge; to be rajasam, originating from rajas; yat, which; sarvesu bhutesu, amidst all things; vetti, apprehends-since knowledge cannot be an agent of hends-since knowledge cannot be an agent of action, therefore the meaning implied is, ‘that, knowledge…through which one apprehends…’-; nana-bhavan, the different entities; prthagvidhan, of various kinds, i.e., those possessing diverse characteristics and different from oneself; prthakrvena, as distinct, as separate in each body.

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

18-20-22 Sarvabhutesu etc. upto samudahrtam. In the classified ones : i.e., [classified] as gods, human beings, etc. Considers as [really] different : i.e., with the thought ‘Here on this depends my pleasure; here in that lies my displeasure’. Without reason : To take recourse to wrath, desire etc., slavishly under the influence of one’s own addiction and also without examining the cause, in named as a thing born of the Tamas (Strand).

Sanskrit Shloka Without Transliteration Marks:

prthaktvena tu yaj jñanam
nana-bhavan prthag-vidhan
vetti sarvesu bhutesu
taj jñanam viddhi rajasam

Sanskrit to English Word for Word Meanings:

pṛthaktvena — because of division; tu — but; yat — which; jñānam — knowledge; nānā-bhāvān — multifarious situations; pṛthak-vidhān — different; vetti — knows; sarveṣu — in all; bhūteṣu — living entities; tat — that; jñānam — knowledge; viddhi — must be known; rājasam — in terms of passion.