In plain words
Here only Prajñā remains. By this Prajñā alone he keeps knowing his own being, that he exists. Afterwards he goes on experiencing Ānanda. All the senses stay stilled. Within the form of the in-breath and the out-breath, the Paramātma, the vessel of Prajñā, experiences it. Because the embodiment of Prajñā is Brahman itself, it has been declaring, ‘Prajñānaṃ brahma’. They have shown this very Prajñā to be the understanding that is ever present in us, and lasting Ānanda. Because this Prajñā, in the waking state, is evenly present in the body, in the antaḥkaraṇa joined with the senses and in the Ātma, they called it constant Integrated awareness. Because he is the embodiment of this Prajñā, they named him Prājña. So Prājña is simply a form of Brahman. That itself is the form of the Ātma. We may doubt, “This form of Brahman, this form of the Ātma, is not to be seen!”; but because the form of the Praṇava is present there too, these forms of Brahman and the Ātma are not apart. In what way does the Praṇava appear to us? It is heard. The Praṇava is not something to be seen. It is what feeds Bhakti. The Oṃkāra is what makes itself heard. This visible world, the sound that is heard, the words that are felt, the heart that makes us experience: all of these lie merged in this Praṇava. Even in this deep sleep, in suṣupti, our breathing in and out goes on. The one whose form is this in-breath and out-breath is himself the embodiment of the Oṃkāra. So this Oṃkāra keeps revealing this form of Brahman and this form of the Ātma. The whole of creation is filled with the Oṃkāra alone. That is why, because even in this suṣupti he remains in the form of Prājña, it shows the Ātma as though made manifest in it.
The fourth is turīya. The turīya state means the fourth place. What is this? In what kind of form does it exist? It draws everything into itself and experiences nothing but full Ānanda. It wears the form of Ānanda. It is filled with the Ānanda of Advaita. It is in a state beyond description. That is, jāgrat, svapna, suṣupti and turīya have been held to be the four feet of the Ātma. In the same way, the Oṃkāra too has four feet. A-kāra, u-kāra, ma-kāra; and what is in the turīya state is the adhirata. What does adhirata mean? The very sound that forms the moment a-kāra, u-kāra and ma-kāra join, they call this adhirata. The a-kāra is the first sound of the Oṃkāra. It is the chief foundation of this world of sound. Among the waves of sound it is the chief. It holds the first place among all the letters. It has been believed to be the Virāṭ-svarūpa joined with the waking state. This very one takes shape as Viṣṇu. The a-kāra is the foundation of the waking world. This is the close bond of the Virāṭ-svarūpa. Then, in the dream state, the rakāra, the u-kāra. This u-kāra is the second sound in the Oṃkāra.