Chandogya Upanishad belongs to the Samveda.

The sixth chapter contains the famous mahavakya, Tat Tvam Asi and is regarded as one of the most important of all Upanishadic teachings. Chapter 6 deals with brahman as sat or existence and hence called sat vidya. It establishes that essence of all beings is same, it is that One Truth, One Reality!

The eighth chapter of the Chandogya Upanishad opens by declaring the body is born with as the “city of Brahman”, and in it is a palace that is special because the entire universe is contained within it. Whatever has been, whatever will be, whatever is, and whatever is not, is all inside that palace asserts the text, and the resident of the palace is the Brahman, as Atman – the Self. With the knowledge of the Brahman, one is free from darkness. 

Swami Abhedananda has explored these chapters in-depth in these talks.