How the *Chandogya Upanishad* is unique in several respects

The Chandogya Upanishad, comes in Sama Veda, and has got 627
mantras.  This Upanishad is unique in several respects.

1. The mantras are quoted by Sage Vyasa, liberally in Brahma Sutra.

2. In Srimad Bhagavad Gita, Krishna says that he is Sama Veda among Veda ganam. (Vibhuti Yoga, Ch.10)
3. Kanchi Kamakoti Sri Chandrasekara Saraswathi had said that it is enough if one learned person reads only Chandogya Upanishad.
4. It is one of the primary subjects for study in Veda Patasalas.

When Sri Subramanian. R. went to Tiruvannamalai, the Librarian
of Sri Ramana Maharshi Centenary Library, in Morvi Guest House, told
him that Bhagavan Ramana's self enquiry and the concept of Heart
Centre on the right side of the chest, has been subtly told in Chandogya Upanishad.

The Karmanga Upasana, Chapter 2 of the Upanishad, speaks about
different types of upasanas.  

Panchabhakti Upasana means meditating on symbols (mudras),
five elements, seasons, rivers and animals, five pranas etc.,

Saptabhakti Upasana, speaks about various aspects of meditation,
through seven components of a Sama Mantra.

Omkara Upasana describes meditation on Omkara, Om.

Loka prapti Upasana explains meditation to gain higher lokas, such
as Swarga.

The glory of Omkara is also highlighted and the Upanishad says that Brahma, the creator, meditated on the three worlds and condensed
them into three Vedas which were further condensed into three Vyahritis, songs and these were further condensed into a, u, and ma, the three letters joined together Omkara, or Pranava or AUM or Om.