hamo damastapah shaucham kshaantiraarjavameva cha; Jnaanam vijnaanam aastikyam brahmakarma swabhaavajam.
Serenity, self-restraint, austerity, purity, forgiveness and also uprightness, knowledge,realisation and belief in God are the duties of the Brahmanas, born of their own nature.
This shloka is concentrating on the qualities of a person born with the nature of Brahmin. The first aspect that Lord mentions is serenity, which is calmness, second is self restraint which is nothing but self control, then it is purity, forgiveness and uprightness that are mentioned as the qualities of a person born as Brahmin. Lord also mentions knowledge as an important quality for a Brahmin, also with that it is realization and belief in God which are stated to be as the duties that every Brahmin should perform. Together with all these qualities a person is said to be a Brahmin.
Extending Interpretation to Mankind’s Life!
If you look at qualities required to be a teacher you see that all those mentioned above must be present in a teacher. A teacher should be someone who should be full of knowledge. A teacher should know everything, because a student can ask anything and everything. A teacher should reflect serenity in him and should be self-restraint always. He should also have the qualities of purity, forgiveness and uprightness. A teacher should always be frank with his students and should give honest opinion to the students, and should always forgive the mistakes that they commit. He should be a firm believer of God because, there is nothing a teacher can achieve without the hand of God on him.
Anybody who has the qualities of a Brahman will always choose teaching as his/her profession because the underlying aspect that lies in this noble profession is the service and sacrifice which is a virtue of a Sattwik person. So, every teacher by nature is sattwik. Here am not referring to teachers, who came into teaching because that was the only job they got, but am referring to those who left other professions and have become teachers. Teaching happens at every level and every age, irrespective of your age. You can be a very young person in mid 20s teaching for people who are much elder to you. So, I would equate a teacher to a sattwik person who is a brahmin by birth, but not by the family in which he is born.