Māndukya 1.01

"Om" is the essence of everything. It encompasses the past, present, and future. Everything is indeed Om, and anything beyond these three times is also Om.

Bhāshya 1.01

Testimonials from Pamda-Purana, Bṛhat-Saṃhitā, and Nairguṇya that are closer to the hermeneutic horizon of the Upanishad are quoted to set the right context. Traditionally, the Upanishad mantras are believed to be praises uttered by the god Varuna in the form of a frog to Lord Narayana.
By stating, "All is indeed Om," the completeness of anything else is rejected.
In nature, the transcendence of the three times exists, and is unique, and belongs solely to Lord Hari.

"In the form of a frog, Narayana, who is four-formed, is praised by Varuna. The god meditating on Narayana, with the Pranava, concentrated. Varuna, in the form of a frog, praised the imperishable Hari."

- stated thus in the Padma Purana.

"Om is declared to be Brahman, the imperishable. It is from Om that the world exists, and therefore, Lord Hari is all. This is expressed as the fulfillment of all qualities. In all times - future, past, and present - Hari remains one in form, always eternal. Thus, this explanation of Omkara is proclaimed."

- stated thus in the Bṛhat Saṃhitā.

"Om is uttered because the syllable Om is supreme; thus, allness and completeness are attributes of it, that of Hari, not of any other, anywhere."

- stated thus in the ancient text called 'Nairguṇya'.

"All is indeed Om," thus rejecting the completeness of anything else. The transcendence of the three times belongs solely to it. Even in nature, this transcendence exists, thus qualifying it as unique.