yad yad ācarati śreṣṭhas
tat tad evetaro janaḥ
sa yat pramāṇaḿ kurute
lokas tad anuvartate

Translation of Bhagavad Gita 3.21

Whatever action a great man performs, common men follow. And whatever standards he sets by exemplary acts, all the world pursues.

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

People in general always require a leader who can teach the public by practical behavior. A leader cannot teach the public to stop smoking if he himself smokes. Lord Caitanya said that a teacher should behave properly before he begins teaching. One who teaches in that way is called acarya, or the ideal teacher. Therefore, a teacher must follow the principles of shastra (scripture) to teach the common man. The teacher cannot manufacture rules against the principles of revealed scriptures. The revealed scriptures, like Manu-samhita and similar others, are considered the standard books to be followed by human society. Thus the leader’s teaching should be based on the principles of such standard shastras. One who desires to improve himself must follow the standard rules as they are practiced by the great teachers. The Srimad-Bhagavatam also affirms that one should follow in the footsteps of great devotees, and that is the way of progress on the path of spiritual realization. The king or the executive head of a state, the father and the school teacher are all considered to be natural leaders of the innocent people in general. All such natural leaders have a great responsibility to their dependents; therefore they must be conversant with standard books of moral and spiritual codes.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

In this verse he explains how the people are taught: by following example.

Commentary by Sri Ramanuja of Sri Sampradaya:

3.21 Whatever ‘an eminent man,’ i.e., he, who is famous for his knowledge of all the scriptures and for his observance of the scriptural dictates, performs, others who have incomplete knowledge of the scriptures will also perform, following his example. With regard to any duty which is being performed with all its ancillaries by an eminent personage, the people with incomplete knowledge will do it with the same ancillaries. Therefore for the protection of the world, all acts that are appropriate to one’s station and stage in life must always be performed by an eminent man who is distinguished for his wisdom. Otherwise, the evil generated from the ruin of the large masses of the world (who neglect their duties by following his example), will bring him down, even if he were a follower of pure Jnana Yoga.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

The denial of any possibility in the slaying of any living entity has been established, for all living entities continually maintain their existence through the agency of the immortal soul. Who can that person slay and how? When knowing its eternality which is free from modification, its immutability which is free from decay, unborn being free from birth and indestructible being free from death. For it is impossible to destroy the immortal soul by any means. So who then can factually claim to be the cause of another perishing? There is none who can claim this or by any means achieve this. So the Supreme Lord by clarifying this point is also informing Arjuna to that He is not directing him to slay anyone because the soul is factually never slain.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

One who understands that the eternal soul is incapable of being destroyed who can be slain and how? The word avinasinam means indestructible, nityam means eternal and therefore by its own inherent nature the immortal soul is imperishable without any defects because what is eternal is never in a state of modification. The word defect is commonly used for that which is not of perfection. The physical body of the living entities is not perfect it is defective, thus the word destruction is applicable to the physical body but never to the eternal soul.

Now begins the summation.

The word avinasinam is indicative of one whose body is indestructible. Eternal in form only applies to the Supreme Lord. Unlimited activity is the attribute of being independent, total independence is found only in the case of the Supreme Lord, who being immutable is without any support outside of Himself.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

As to remove any doubts concerning the Vedic injunction against the killing of cows and the killing of a brahmana such as Drona, the perpetrators of these heinious crimes go directly to hell to suffer at the termination of their material existence. To mitigate this Lord Krishna tells Arjuna that one who knows the soul to be indestructible and thus eternal as well as unborn and unmodifiable although uniquely different within every body knows that no one in anyway can cause the destruction of the soul. Who is the doer in the action of killing? Whom can one cause to be killed? Can one be the agent in the death of the soul? The answer is no to all and it is indicated that there should be no doubt about the veracity of the Vedic scriptures regarding the sin incurred either when one causes another to be killed or when one is directed to kill another. By this the Vedic injunctions prohibiting cow slaughter and the slaying of brahmanas and the great sin attached thereof must be accepted as fact even though one is in knowledge about the factual nature of the eternal reality of the souls immortality.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

3.21 Yat yat, [This is according to the Ast. The G1. Pr. reads, yat yat yesu yesu.-Tr.] whatever action; a sresthah, superior person, a leader; acarati, does; itarah, another; janah, person, who follows him; does tat tat eva, that very action. Further, yat, whatever; sah, he, the superior person; kurute, upholds; as pramanam, authority, be it Vedic or secular; lokah, an ordinary person; anuvartate, follows; tat, that, i.e. he accepts that very thing as authoritative. ‘If you have a doubt here with regard to the duty of preventing people from straying, then why do you not observe Me?’

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

3.21 See Comment under 3.22

Sanskrit Shloka Without Transliteration Marks:

yad yad acarati sresthas
tat tad evetaro janah
sa yat pramanam kurute
lokas tad anuvartate

Sanskrit to English Word for Word Meanings:

yat yat — whatever; ācarati — he does; śreṣṭhaḥ — a respectable leader; tat — that; tat — and that alone; eva — certainly; itaraḥ — common; janaḥ — person; saḥ — he; yat — whichever; pramāṇam — example; kurute — does perform; lokaḥ — all the world; tat — that; anuvartate — follows in the footsteps.