BG 3.21

3.21 यद्यत् whatsoever? आचरति does? श्रेष्ठः the best? तत्तत् that? एव only? इतरः the other? जनः people? सः he (that great man)? यत् what? प्रमाणम् standard (authority? demonstration)? कुरुते does? लोकः the world (people)? तत् that? अनुवर्तते follows.Commentary Man is a social animal. He is an imitating animal too. He takes his ideas of right and wrong from those whom he regards as his moral superior. Whatever a great man follows? the same is considered as an authority by his followers. They try to follow him. They endeavour to walk in his footsteps.

— vedicscriptures · exposition · source ↗

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 ācārya, or the ideal teacher. Therefore, a teacher must follow the principles of śāstra (scripture) to teach the common man. The teacher cannot manufacture rules against the principles of revealed scriptures. The revealed scriptures, like Manu-saṁhitā 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 śāstras. One who desires to improve himself must follow the standard rules as they are practiced by the great teachers. The Śrīmad-Bhāgavatam 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 schoolteacher 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.

— vedicscriptures · exposition · source ↗