First of all, a teacher must know his profession thoroughly. He must know his subject beyond the point he intends to teach. He needs to be an expert. For example, if he is teaching literature, he should know all the plays of Shakespeare - or at least most of them, rather than just the play he is teaching. He can then make cross references and answer all the questions that arise in the minds of his students. Knowing his subject is of no use if he does not know how, or not bother to, to teach it most effectively to his students. Though it is true that in a secondary school, student should take the responsibility for their own learning, it would be dull and boring to learn from a teacher who does not present his subject in an interesting manner.
It is the teacher's duty to promote love of his subject among his students. This he will do first by loving the subject himself. His enthusiasm and love for his subject will catch on with his students and if they learn to love a subject they can learn it better. A bad teacher, usually by his lack of enthusiasm and interest, will cause his subject to be hated. it is fir such reason that a teacher should adopt good teaching methods instead of resorting to easier methods like just reading out of textbook.
Every teacher must be genuinely interested in his job. He must feel that it is his calling to develop young minds, and through them, to actually shape the destiny of the country and the world. He must be dedicated and caring at least to the point that it matters to him that his students learn all that they need to know.
Over and above teaching his subject, a teacher has the responsibility to develop characters of the students in his life. Quite often, a teacher is a student's role model. All of us who go through school, hero worship at least one teacher whom we would like to emulate. A teacher should always be aware of this responsibility. If by chance he were to show flexibility in ethics and morals, he is more or less giving a sanction to his charges that it is acceptable for them to e like that too. This applies to simple vices like smoking and more serious errors where the teacher fails to draw a clear line between good and bad behaviour.
From this time immemorial, teachers have been the pillars of society. Staying in the background, at least for most of the time, they have been indirectly responsible for the advancement of the race. Often, it is their lot to go unnoticed. But time and again, all great men and women have been unsparing in their praise of teachers. this is by far their greatest responsibility: teachers are the ones who guarantee that our tomorrows will be as hood as, id not better than, our todays. By shaping characters they ensure that the world continues to be.