In the teacher we must first see that he knows the secret of the scriptures. The whole world reads scriptures — Bibles, Vedas, Korans, and others; but they are only words, external arrangement, syntax, the etymology, the philology, the dry bones of religion. The teacher may be able to find what is the age of any book, but words are only the external forms in which things come. Those who deal too much in words and let the mind run always in the force of words lose the spirit. So the teacher must be able to know the spirit of the scriptures. The network of words is like a huge forest in which the human mind loses itself and finds no way out. The various methods of joining words, the various methods of speaking a beautiful language, the various methods of explaining the dicta of the scriptures, are only for the enjoyment of the learned. They do not attain perfection; they are simply desirous to show their learning, so that the world may praise them and see that they are learned men. You will find that no one of the great teachers of the world went into these various explanations of texts; on their part there is no attempt at "text-torturing", no saying, "This word means this, and this is the philological connection between this and that word." You study all the great teachers the world has produced, and you will see that no one of them goes that way. Yet they taught, while others, who have nothing to teach, will take up a word and write a three-volume book on its origin and use. As my Master used to say, what would you think of men who went into a mango orchard and busied themselves in counting the leaves and examining the colour of the leaves, the size of the twigs, the number of branches, and so forth, while only one of them had the sense to begin to eat the mangoes? So leave this counting of leaves and twigs and this note-taking to others. That work has its own value in its proper place, but not here in the spiritual realm. Men never become spiritual through such work; you have never once seen a strong spiritual man among these "leaf-counters". Religion is the highest aim of man, the highest glory, but it does not require "leaf-counting". If you want to be a Christian, it is not necessary to know whether Christ was born in Jerusalem or Bethlehem or just the exact date on which he pronounced the Sermon on the Mount; you only require to feel the Sermon on the Mount. It is not necessary to read two thousand words on when it was delivered. All that is for the enjoyment of the learned. Let them have it; say amen to that. Let us eat the mangoes.

The second condition necessary in the teacher is that he must be sinless. The question was once asked me in England by a friend, "Why should we look to the personality of a teacher? We have only to judge of what he says, and take that up." Not so. If a man wants to teach me something of dynamics or chemistry or any other physical science, he may be of any character; he can still teach dynamics or any other science. For the knowledge that the physical sciences require is simply intellectual and depends on intellectual strength; a man can have in such a case a gigantic intellectual power without the least development of his soul. But in the spiritual sciences it is impossible from first to last that there can be any spiritual light in that soul which is impure. What can such a soul teach? It knows nothing. Spiritual truth is purity. "Blessed are the pure in heart, for they shall see God". In that one sentence is the gist of all religions. If you have learnt that, all that has been said in the past and all that it is possible to say in the future, you have known; you need not look into anything else, for you have all that is necessary in that one sentence; it could save the world, were all the other scriptures lost. A vision of God, a glimpse of the beyond never comes until the soul is pure. Therefore in the teacher of spirituality, purity is the one thing indispensable; we must see first what he is, and then what he says. Not so with intellectual teachers; there we care more for what he says than what he is. With the teacher of religion we must first and foremost see what he is, and then alone comes the value of the words, because he is the transmitter. What will he transmit, if he has not flat spiritual power in him? To give a simile: If a heater is hot, it can convey heat vibrations, but if not, it is impossible to do so. Even so is the case with the mental vibrations of the religious teacher which he conveys to the mind of the taught. It is a question of transference, and not of stimulating only our intellectual faculties. Some power, real and tangible, goes out from the teacher and begins to grow in the mind of the taught. Therefore the necessary condition is that the teacher must be true.

The third condition is motive. We should see that he does not teach with any ulterior motive, for name, or fame, or anything else, but simply for love, pure love for you. When spiritual forces are transmitted from the teacher to the taught, they can only be conveyed through the medium of love; there is no other medium that can convey them. Any other motive, such as gain or name, would immediately destroy the conveying medium; therefore all must be done through love. One who has known God can alone be a teacher. When you see that in the teacher these conditions are fulfilled, you are safe; if they are not fulfilled, it is unwise to accept him. There is a great risk, if he cannot convey goodness, of his conveying wickedness sometimes. This must be guarded against; therefore it naturally follows that we cannot be taught by anybody and everybody.

Excerpts from Swami Vivekananda's writing The Teachers of Spirituality[Source]