I started reading an explnation (its called teeka in Hindi) on Isa Upanishad. This is said to be the first Upanishad. Every Upanishad has a seed mantra. It is said that if you learn seed mantra you have learned the Upanishad. Isa Upanishad has below seed mantra :
Aum
Purnamadah
Purnamidam
Purnat Purnamudachyate
Purnasya Purnamadaya
Purnameva Vashishyate
Meaning:
Aum
That Is The Whole.
This Is The Whole.
From Wholeness Emerges Wholeness.
Wholeness Coming From Wholeness,
Wholeness Still Remains.
Source: http://www.jaicobooks.com/j/j_searchtry.asp?selcat=title&keyword=i+am+that
