In plain words
They went on commanding this tongue, given to humanity, to speak sacred words. The mantra went on teaching that the brahmacārī must not speak Asatya, must not talk too much, must not stir up quarrels between one another, must not speak ill of others; that these are the four sins the tongue commits; and so, that he should guard himself from falling prey to these four sins. When he develops such good qualities in his life, the whole of the future takes shape as a royal road. The second, the Brāhmaṇa. What brings us to recognise the truth of how we should use these mantras, what this mantra's power is and what fruit it gives, is the Brāhmaṇa. Because they uttered such mantras with their meaning, those scholars got the name ‘brahmins’. This they held to be the householder's Dharma. They went on teaching that the householder, uttering mantras with their meaning, for the welfare of the world, in order to drive away calamities such as too much rain and drought that come up in daily life, and in order to win heaven, should become the embodiment of the whole community and shape his life into an ideal. So they held the householder's Dharma to be very sacred. Carrying out this householder's Dharma well, he gradually enters vānaprastha. The principle of this vānaprastha itself they named ‘Āraṇyaka’. That is, not living in a house or in a town, but spending their life peacefully in the forests or groves nearby, and making the rest of their life fruitful through thinking of God. Because they spent their time in the forests and practised sacred contemplation of the Paramātma, this Vedic Dharma came by the name ‘Āraṇyakas’. Then, the fourth, the Upaniṣads. This word carries many wonderful meanings. In it the chief word is ‘ṣat’. That is, it has many meanings: sitting, moving, destroying, taking refuge. But we have to take the meaning of that word according to the time and the context. Here we need to take the meaning ‘sitting’ for the word ‘ṣat’.