In plain words
That is, when we look with the body-minded outlook, it takes shape as nothing but a darkness. But we must see the turīya state with the Ātma-minded outlook. Only then can we experience its state of absorption. This very turīya state they have called samādhi. This is the supreme goal of man. These states, jāgrat, svapna, suṣupti and turīya, are like the four feet of the Ātma.
In just the same way the Oṃkāra has four feet. These four are the A, the U, the M and the amātra. They have also held this amātra state to be the turīya state. This A, become speech, has spread through the whole world. That is why it has reached the level of the universe. That is why we may call it Viśva. The reason is that it is joined with Śabda-Brahman. The U is utterance. It is joined with a divine radiance. Then the M is the last part of the Oṃkāra. It is joined with prajñā. The joining of the three, A, U and M, they named the amātra state. This itself they called the Oṃkāra. These four are the four feet of the Oṃkāra.
So, when we inquire well into human nature, what is the Ātma? The Ātma means the oneness of the three, speech, body and prāṇa: that is the Ātma. The joining of these three is the Ātma. In this, the principle of the mind is joined with the body. Speech is full of radiance. The mind is made of food. Then prāṇa is made of rasa. Radiant speech keeps joining the body made of food in the radiance made of rasa, that is, in speech. It keeps joining Brahman. That is, radiant speech stays joined, within the body made of food, with the rasa made of prāṇa. This very principle of Brahman the Upaniṣads have described as rich in the eight splendours.
Made of Śabda-Brahman, of all that moves and moves not, of light, of speech, made of eternal Ānanda, of what is beyond the beyond, of Māyā, of Śrī, made of the eight splendours, of Sadāśiva, of Śrī Śiva-Śakti-Sai.
In this world there is not one thing that is not Brahman. The whole world is full of Brahman. That is why we have to believe that the principle of the Ātma is, in this, simply the Oṃkāra, Brahman, the principle that pervades the universe.
They have said that speech is the Ṛg Veda, the mind the Yajur Veda and prāṇa the Sāma Veda.